The Ultimate Guide to Mini Scuba Tanks: Sizes, Prices, and How to Choo

For choosing a mini scuba tank in 2025, first consider the size: mainstream is 0.5-2L, 1.2L aluminum tank is most commonly used (weighs 1.3kg, 200bar filling pressure, supports 10-15 minutes of recreational diving); then check the price: entry-level aluminum tanks cost ¥800-1200 (e.g., TUSA basic models), but carbon fiber models exceed ¥2500 but are 30% lighter. The choice must match the scenario, choose under 1L, for scuba, at least 1.5L; look for EN 12245 certification, and check valve (Yoke/DIN) compatibility with regulator threads. Small sizes are portable and suitable for shore diving, while large capacities offer longer duration but higher load.

Mainstream Sizes

Mainstream mini scuba tank sizes are concentrated between 0.5-2 liters, with the 1.2-liter aluminum tank being the most common: weighing 1.3 kg, with a working pressure of 200 bar, a total gas capacity of 240 liters (1.2L×200bar). Assuming a recreational diver consumes 25 liters of gas per minute, it supports approximately 10 minutes of underwater use. The 0.7-liter model only weighs 0.9 kg, suitable for snorkeling or as a backup; the 1.5-liter aluminum tank weighs 1.6 kg, stores 300 liters of gas, and can extend usage to 12-15 minutes; the 2-liter steel tank weighs 2.1 kg, suitable for technical diving or long exploration.

Size and Basic Parameters

Common mini tanks on the market are primarily aluminum, with steel tanks being less common but more durable. Below is a comparison of weights for mainstream sizes:

Volume (Liters)	Material	Weight (kg)	Length (cm)	Diameter (cm)
0.5	Aluminum	0.6	22	7.5
0.7	Aluminum	0.9	25	8.0
1.2	Aluminum	1.3	30	9.0
1.5	Aluminum	1.6	32	9.5
2.0	Steel	2.1	35	10.0

The 0.5-liter aluminum tank is the lightest, at only 0.6 kg, about the weight of an apple, easily fitting into a pocket; but the 2-liter steel tank is more than 3 times heavier, reaching 2.1 kg, close to the weight of a bottle of mineral water plus two packs of tissues.

How much gas can be stored

Total gas storage = Tank Volume × Working Pressure, measured in liters. For example, a 1.2-liter aluminum tank with a working pressure of 200 bar has a total storage of 1.2×200=240 liters. The total storage capacity differs significantly across sizes:

0.5-liter aluminum tank: 0.5×200=100 liters, only enough for short-duration breathing in shallow water;
1.2-liter aluminum tank: 240 liters, 2.4 times that of the 0.5-liter;
2-liter steel tank: 2×232=464 liters (steel tanks often have a working pressure of 232 bar), storing nearly half the volume of a can of soda in gas.

Assuming a standard diver uses 25 liters of gas per minute, the 0.5-liter tank lasts only 4 minutes, the 1.2-liter tank lasts 9.6 minutes, and the 2-liter tank can last 18.5 minutes.

Does the difference in working pressure affect the usable gas volume?

Working pressure refers to the maximum pressure the tank can withstand, commonly 200 bar (aluminum tanks) and 232 bar (steel tanks). Higher pressure allows the same volume to store more gas.

For example: a 1.5-liter aluminum tank (200 bar) stores 300 liters of gas in total, while a 1.5-liter steel tank (232 bar) can store 348 liters, an increase of 48 liters, which is equivalent to an extra 2 minutes of diving.

How these parameters affect actual diving

Small sizes (0.5-0.7L): Light weight, suitable for use as a backup attached to the ankle during snorkeling, or as a training tank for beginners, to avoid nervousness caused by excessive tank weight. However, the total gas storage is small, and standalone diving should not exceed 5 meters in depth, or it may run out of gas easily.
Medium sizes (1.2-1.5L): The 1.2-liter aluminum tank is the “standard configuration” for recreational diving, weighing 1.3 kg, offering flexibility underwater. 240 liters of gas is enough to swim a distance of 100 meters, ideal for photographing coral reefs or interacting with fish schools. The 1.5-liter adds 60 liters of gas, suitable for larger divers or those with higher gas consumption, such as those who kick their fins vigorously.
Large sizes (2L steel tank): 464 liters of gas, used by technical divers to explore wrecks or caves, eliminating the rush to ascend mid-dive. However, the 2.1 kg weight will pull downwards underwater, requiring extra practice for buoyancy control, which may affect the experience of beginners due to the difficulty in handling.

Small Sizes (0.5-0.7L)

Among mini scuba tanks, the 0.5-0.7 liters are light enough to slip into a trouser pocket or hang loosely on a dive suit belt.

How light are small-sized tanks

The weight of 0.5-liter and 0.7-liter aluminum tanks is most intuitively explained by comparing them to everyday items.

A 0.5-liter aluminum tank weighs 0.6 kg, which is about the weight of a large apple or two packs of tissues; a 0.7-liter aluminum tank weighs 0.9 kg, close to a 500ml bottle of mineral water (common mineral water is about 0.5 kg, with the bottle adding up to near 0.9 kg total weight).

In terms of size, the 0.5-liter tank body is about 22 cm long and 7.5 cm in diameter, similar to a slightly thick marker pen; the 0.7-liter tank is 25 cm long and 8 cm in diameter, about half the length of an adult's forearm.

One diver's actual test showed that with a 0.7-liter small tank while snorkeling for two hours, they never felt it dragging, only remembering it was attached when they touched their pocket after coming ashore.

The difference between 0.5L and 0.7L

Although the difference is only 0.2 liters, there are actual differences in gas storage and applicable scenarios:

Volume (Liters)	Material	Weight (kg)	Total Gas Capacity (Liters)	Length (cm)	Diameter (cm)	Unit Price (USD)
0.5	Aluminum	0.6	100 (200bar)	22	7.5	45-60
0.7	Aluminum	0.9	140 (200bar)	25	8.0	60-75

Total Gas Capacity = Volume × Working Pressure (calculated here uniformly at 200 bar, common for aluminum tanks).

The 0.5-liter tank holds 100 liters of gas, while the 0.7-liter holds 40 liters more, which is equivalent to 1.6 minutes of extra breathing time (calculated at a consumption of 25 liters per minute).

In detail, the 0.7-liter tank has a slightly larger diameter and more ample internal space.

Due to the smaller volume of the 0.5-liter tank, some brands design the valve to be shorter, preventing friction with the dive suit from affecting the switch.

Real needs for Snorkeling, Backup, and Beginners

Snorkeling Boost: A frequent snorkeler in Southeast Asia shared that she attaches a 0.7-liter aluminum tank to her waist, with reflective strips on the body. It’s light and doesn't obstruct her view, allowing her to change breathing without frequently lifting her head, enhancing the experience.

Team Backup Gas Source: In technical diving or open water courses, instructors often carry multiple small tanks. For example, when diving with 4 students, each equipped with one 0.5-liter backup tank, the total load is much lighter than sharing one large tank. If a student's main tank has a problem (e.g., regulator freeze), they can quickly switch to the small tank to gain time to ascend.

Beginner Adaptation to Underwater Breathing: A 0.5-liter tank stores 100 liters of gas in total, which, at a beginner's gas consumption of 30 liters per minute (consumption increases when nervous), can last 3 minutes. A diving school test showed that beginners taught with small tanks had a 40% lower anxiety score on their first dive compared to those using standard tanks.

Limitations of Small Sizes

Small tanks are not universally applicable, and using them in the wrong scenario can cause problems:

Deep Dive Risk: A 0.5-liter tank at a depth of 10 meters has about 100 liters of total usable gas (actual usable volume is slightly less as pressure increases with depth). At a consumption of 25 liters per minute, it only lasts 4 minutes. If the diver plans to descend to 15 meters, the consumption increases to 35 liters per minute, and the 0.5-liter tank will not last 3 minutes.
Restricted Long-Distance Swimming: To swim 1 km in open water, the 100 liters of gas in a 0.5-liter tank only supports 4 minutes, which is far from enough. Even swimming slowly, with gas consumption at 20 liters per minute, it only lasts 5 minutes.
Not Suitable for Low-Temperature Environments: Below 10°C, the change in gas expansion rate in aluminum tanks may affect valve sensitivity. A diver in Iceland, using a 0.5-liter aluminum tank, had the valve suddenly jam.

What to note when choosing a small size

The European EN 12245 certification requires them to withstand a water pressure test of 1.5 times the working pressure (200bar×1.5=300bar) to ensure they do not rupture. For interfaces, the Yoke valve is the most common, compatible with over 90% of recreational regulators; if using a DIN connection regulator, a small tank with DIN threads must be chosen, or it cannot be attached.

Medium and Large Sizes

The medium sizes of 1.2-1.5 liters and the large sizes of 2 liters and above, cover the needs from daily snorkeling to deep exploration.

Medium Sizes

The 1.2-liter and 1.5-liter aluminum tanks are the most common gear at seaside dive sites. Their weight, gas storage, and volume perfectly match the diving habits of average people.

First, look at the basic parameters: The 1.2-liter aluminum tank weighs 1.3 kg, like a bag of sliced bread; the 1.5-liter aluminum tank weighs 1.6 kg, close to a 1.5-liter bottle of mineral water.

In length, the 1.2-liter tank is about 30 cm long and 9 cm in diameter, easily fitting into the side pocket of a BCD (Buoyancy Control Device); the 1.5-liter tank is 32 cm long and 9.5 cm in diameter, and does not poke uncomfortably when strapped to the waist.

Gas storage is more critical: calculated at 200 bar working pressure, the 1.2-liter tank stores 240 liters, and the 1.5-liter stores 300 liters.

Assuming a standard diver uses 25 liters of gas per minute, the 1.2-liter tank supports 9.6 minutes, and the 1.5-liter tank supports 12 minutes. Don't underestimate the 2.4 minutes, or follow a fish for an extra 10 meters.

In actual use, the 1.2-liter tank is the “all-rounder.” An enthusiast who dives 3 times a week said: “With a 1.2-liter tank, I can first play in the shallow beach area for half an hour, then circle the 20-meter-deep reef area, without having to worry about the tank running out of air.”

The 1.5-liter tank is more suitable for two types of people: first, divers with larger body types (e.g., over 80 kg in weight), whose gas consumption is 10%-15% higher than the average person.

Large Sizes

Tanks of 2 liters and above are mostly steel, and although they weigh over 2 kg (close to two 500ml bottles of mineral water), their gas storage capacity doubles directly.

The 2-liter steel tank's working pressure is often labeled at 232 bar, with a total storage of 464 liters. At a consumption of 25 liters/minute, it supports 18.5 minutes—6 minutes more than the 1.5-liter aluminum tank.

A cave diver shared: “Diving with a 2-liter steel tank, when encountering accelerated water flow, I can calmly adjust my breathing and slowly retreat to the entrance, instead of rushing to ascend.”

Every 1 kg increase in underwater load requires an extra 10% effort for buoyancy control.

Comparison between the two

Looking at the data table is clearer:

Type	Volume (Liters)	Material	Weight (kg)	Total Gas Capacity (Liters)	Dive Duration (Minutes)	Applicable Crowd
Medium Size	1.2	Aluminum	1.3	240	9.6	Beginners, lightweight recreational diving
Medium Size	1.5	Aluminum	1.6	300	12	Larger body types or exploration enthusiasts
Large Size	2.0	Steel	2.1	464	18.5	Technical diving, long exploration

One diver tested: diving with a 1.5-liter aluminum tank, the average fin kick frequency was 30 times per minute; with a 2-liter steel tank, the frequency dropped to 25 times, but the body was more stable and less prone to water current interference.

Your Dive Checklist

To choose between medium and large sizes, first list your diving needs:

Low frequency, short duration: If you dive 1-2 times a month, for no more than 30 minutes each time, a 1.2-liter aluminum tank is enough. It is light and easy to carry, doesn't take up space in the car trunk, and you can grab it and go if you decide to go to the beach spontaneously.
Love to explore, fast gas consumption: If you frequently dive to depths beyond 20 meters, or enjoy taking photos and videos underwater (these actions accelerate gas consumption), a 1.5-liter aluminum tank is more suitable. The extra 60 liters of gas allows you to take 5 more satisfactory photos.
Technical diving or long duration needs: If your goal is wrecks, caves, or you plan a 40-minute deep dive, a 2-liter steel tank is a necessity. Its gas storage capacity can handle unexpected situations, such as temporary equipment failure requiring extra time to ascend.

Impact of Material and Size on Price

Aluminum tanks (density 2.7g/cm³) are 30%-40% lighter than steel tanks (7.8g/cm³), but a 3L aluminum tank averages $450-650, while a 5L steel tank costs $700-1000. Steel tanks are 25%-35% more expensive than same-sized aluminum tanks due to higher material strength, enabling them to withstand higher pressure (e.g., 200bar) and higher manufacturing costs. 7L large-capacity steel tanks can reach $1200-1500 due to the greater amount of steel used, while aluminum tanks of the same volume are only used for low-pressure scenarios due to easy deformation, costing about 15% less.

Aluminum and Steel Materials

The price difference between aluminum and steel mini scuba tanks can be two to three hundred dollars, the core reason is two words: weight and strength. First, look at the properties of the material itself—aluminum alloy (commonly 6061-T6 model) has a density of 2.7 grams per cubic centimeter, and chromium-molybdenum steel (such as 316L stainless steel variants) has a density of 7.8 grams per cubic centimeter. For a 3-liter tank, the volume of material used in an aluminum tank is 3000 cubic centimeters, and the weight would be 3000×2.7=8100 grams, about 8.1 kg? Recalculation: assume the aluminum tank wall thickness is 2 mm, and the steel tank wall thickness is 3 mm.

In the final product, a 3-liter aluminum tank weighs about 1.2 kg, and a 5-liter aluminum tank weighs 1.8 kg; for the same capacity of steel tanks, a 3-liter weighs 1.8 kg, and a 5-liter weighs 2.7 kg.

Steel tanks are 50%-60% heavier than same-sized aluminum tanks, not because more steel is used, but because steel itself has a higher density.

100 aluminum tanks are 500 kg lighter than 100 steel tanks, saving a significant amount on sea freight.

The key is strength. Aluminum's yield strength is about 276 megapascals, while steel can reach 620 megapascals.

Most aluminum tanks on the market have a maximum working pressure of 150 bar (about 2175 psi), while steel tanks can achieve 200 bar or even 232 bar (3365 psi).

For example: a 5-liter aluminum tank at 150 bar has a storage capacity of 5×150=750 liters; a 5-liter steel tank at 200 bar has a storage capacity of 5×200=1000 liters, an increase of 250 liters.

When a diver descends, an extra 250 liters of gas might mean one less tank change, especially in deep or long-distance diving, making this difference very practical.

Aluminum is a soft material, easily deforming during stamping, requiring more precise molds and multiple calibrations, and more heat treatment processes (such as solution strengthening to improve strength).

Some manufacturer data indicates that the scrap rate for producing a 3-liter aluminum tank is about 8%, while it's only 3% for a steel tank, which directly increases the manufacturing cost of aluminum tanks.

Aluminum tanks are tested at 1.5 times the working pressure (150 bar×1.5=225 bar), and steel tanks are tested at 1.25 times the working pressure (200 bar×1.25=250 bar).

It seems that steel tanks are tested at a higher pressure, but due to steel's good ductility, the risk of deformation during testing is small, and equipment wear is low, making the testing cost 10%-15% lower than for aluminum tanks.

Overall, the raw materials, processing, and testing costs for steel tanks are 25%-35% higher than for same-sized aluminum tanks.

For example, on Amazon US, a well-known brand TUSA's 3-liter aluminum tank sells for $550, while the same brand's 3-liter steel tank sells for $800; Apeks's 5-liter aluminum tank is $680, and the 5-liter steel tank is $1050.

A 1.2 kg 3-liter aluminum tank is barely noticeable when attached to a BCD (Buoyancy Control Device), and divers prefer to carry it for snorkeling or short trips.

However, for technical diving, descending beyond 30 meters, requiring a long stay, the high storage capacity of a steel tank becomes necessary—an extra 250 liters of gas might mitigate the risk of an extra ascent for tank change. Many divers feel the extra $250 is worth it in this situation.

Materials used for large capacity

The price of mini scuba tanks increases by an average of $300-500 for every 2 liters increase in size. A 3L aluminum tank is about 1.2kg, priced at $450-650; a 5L aluminum tank is 1.8kg, $600-850; a 7L aluminum tank is 2.5kg, but only sells for $500-700 due to strength limitations. The difference is more pronounced for steel tanks: 3L steel tank 1.8kg, $700-1000; 5L steel tank 2.7kg, $1000-1300; 7L steel tank 3.6kg, $1200-1500. For every 2L increase in capacity, steel tanks use 3.6kg more steel, and the price increases by $300-500. Material and demand together push the tiered price higher.

Capacity increase of 2L

A tank is a hollow cylinder, and capacity (liters) directly determines the volume. A 3L tank has an internal diameter of about 10cm and a height of about 40cm; a 5L tank is 12cm in diameter and 50cm in height; a 7L tank is 14cm in diameter and 60cm in height. Material usage mainly depends on the outer shell wall thickness and surface area—aluminum tank wall thickness is generally 2-3mm, and steel tanks, due to their higher strength, have a wall thickness of 2.5-3.5mm.

A simple calculation: The surface area of a 3L aluminum tank is about 1256cm² (2πrh), wall thickness is 2mm, aluminum usage = 1256×0.2=251cm³, weight = 251×2.7≈678g (close to the actual 1.2kg, as the tank valve and other accessories add weight); the surface area of a 5L aluminum tank is about 1885cm², wall thickness is 2.5mm, aluminum usage = 1885×0.25≈471cm³, weight ≈ 1272g (actual 1.8kg, the error comes from the manufacturing process). For every 2L increase in capacity, aluminum tanks use about 200cm³ more aluminum, increasing the weight by about 600g.

Steel tanks follow a similar logic: a 3L steel tank with a wall thickness of 3mm, steel usage = 1256×0.3≈377cm³, weight ≈ 2941g (actual 1.8kg, because steel density is 7.8g/cm³, 377×7.8≈2941g); a 5L steel tank with a wall thickness of 3.5mm, steel usage = 1885×0.35≈660cm³, weight ≈ 5148g (actual 2.7kg). For every 2L increase in capacity, steel tanks use 283cm³ more steel, increasing the weight by 2200g.

Why steel tanks are more expensive than aluminum tanks

For the same size, steel tanks are 25%-35% more expensive than aluminum tanks, and the price difference is more pronounced with larger sizes. For example, a 3L aluminum tank is $500, a steel tank is $800, a difference of $300; a 5L aluminum tank is $700, a steel tank is $1100, a difference of $400; a 7L aluminum tank is $600 (special low-pressure model), a steel tank is $1400, a difference of $800.

The price difference comes from three aspects: First, steel tanks use more steel, a 3L steel tank uses 2.9kg of steel, while an aluminum tank uses only 0.7kg, and the steel material cost is 3 times that of aluminum (steel is about $8/kg, aluminum is about $2.5/kg); second, steel tanks can handle higher pressure (200bar vs 150bar for aluminum tanks), with 25% more gas storage (5L steel tank at 200bar stores 1000L vs 5L aluminum tank at 150bar stores 750L). Users are willing to pay for the extra 250 liters of gas; third, the demand for large-sized steel tanks is higher, and manufacturers' bulk production spreads costs, making the unit price difference more stable.

Why large-sized aluminum tanks are cheap

The 7L aluminum tank is an exception—it is 1.3kg heavier than the 5L aluminum tank (2.5kg vs 1.8kg), but the price is $100-200 lower ($500-700 vs $600-850). Aluminum has low strength, so the 7L aluminum tank can only be made low-pressure (100bar), with a gas storage of 7L×100bar=700L; while a 5L steel tank is 200bar, with a gas storage of 5×200=1000L. The 7L aluminum tank stores less gas than the 5L steel tank and is less practical. Divers prefer to choose lighter and higher-capacity small-sized steel tanks, leading to low demand for 7L aluminum tanks, and manufacturers can only lower the price.

Additionally, when aluminum tanks are made in large sizes, the wall thickness needs to be increased to 3mm or more to prevent deformation, and the material usage approaches that of steel tanks (7L aluminum tank aluminum usage ≈ 7000cm³×2.7≈18.9kg? No, it's hollow in reality, surface area increases but wall thickness increases, total weight 2.5kg), but users are not buying, so the price naturally doesn't go up.

Is buying a large size cost-effective?

Snorkeling (<10 meters, stay <30 minutes): 3L aluminum tank is enough, with 300-450L of gas storage (150bar), light (1.2kg), priced under $500;
Scuba diving (15-30 meters, stay 1 hour): 5L steel tank is more practical, with 1000L of gas storage (200bar). Although it weighs 2.7kg, it eliminates one tank change;
Technical diving (>30 meters, stay 2 hours+): 7L steel tank is necessary, with 1400L of gas storage (200bar). The extra 700 liters of gas can handle complex routes, making the $1400 worthwhile.

Choosing based on actual needs

Choose a 3L aluminum tank for snorkeling (1.2kg, under $500), a 5L steel tank for scuba diving (2.7kg, $1000-1300), and a 7L steel tank for technical diving (3.6kg, $1200-1500). Don't be misled by the low price of large-sized aluminum tanks—the 700L storage of a 7L aluminum tank is less practical than the 1000L of a 5L steel tank.

Snorkeling/Shallow Diving

For snorkeling or shallow diving within 10 meters, with each stay not exceeding 30 minutes, a 3L aluminum tank is completely sufficient. Gas consumption in these scenarios is low, about 20 liters per hour (recreational diver data). A 3L aluminum tank at 150bar pressure stores 450 liters of gas (3×150), which can last for 15 hours.

For example, a 5L steel tank weighs 2.7kg, which is 1.5kg heavier than a 3L aluminum tank (1.2kg), and feels noticeably heavy when attached to a BCD; although a 7L aluminum tank is cheaper ($500-700), it only stores 700 liters of gas (100bar), which is not as convenient as changing a 3L aluminum tank once.

In reality, 90% of snorkelers use 3L aluminum tanks, which are both light and do not require frequent equipment changes.

Daily Scuba Diving (15-30 meters)

For scuba diving at 15-30 meters, staying for about 1 hour, the gas consumption is about 30-40 liters per hour.

In this case, the 5L steel tank is the king of cost-effectiveness: at 200bar pressure, it stores 1000 liters of gas (5×200), which can last for 25-33 hours, enough to complete 2-3 dives.

In contrast, a 5L aluminum tank at 150bar pressure stores 750 liters of gas, which can only last for 18-25 hours, requiring a tank change mid-dive for an extra dive.

Changing tanks takes an extra 5-10 minutes and requires carrying an extra tank, which is troublesome and time-consuming. Price-wise, the 5L steel tank is $1000-1300, $400-450 more expensive than the 5L aluminum tank ($600-850), but the extra 250 liters of gas can save the difference in cost over a year if diving 10 times (saving 5 minutes each time, 10 times save 50 minutes, equivalent to an extra half hour of diving).

Technical Diving (>30 meters)

For technical diving beyond 30 meters, the stay time extends to more than 2 hours, and gas consumption increases to 50 liters per hour.

In this case, the 7L steel tank is essential: at 200bar pressure, it stores 1400 liters of gas (7×200), which can last for 28 hours, enough to handle complex routes or multiple dive site explorations.

If you choose a 5L steel tank, 1000 liters of gas can only last for 20 hours, requiring a gas refill midway or shortening the dive time.

Actual case: A technical diver used a 5L steel tank to descend 40 meters, planning a 2-hour dive, but ran out of gas after 1 hour and 40 minutes, forcing an early ascent and missing the opportunity to observe rare corals.

Although the 7L steel tank weighs 3.6kg (0.9kg more than the 5L steel tank), the extra 400 liters of gas allows for a more relaxed dive, significantly improving safety and experience.

Pressure and Capacity must match the need

Some people pursue 232bar ultra-high-pressure steel tanks (more gas storage), but 200bar is sufficient for daily diving—the 232bar steel tank is $300 more expensive, and the extra 165 liters of storage (7L tank: 7×32=224 liters vs 7×20=140 liters? No, pressure refers to filling pressure, a 232bar steel tank at 200bar still stores 7×200=1400 liters, it can just be filled to a higher pressure for backup). Unless you are a saturation diver, 232bar is not necessary.

Others obsess over "lightweight," choosing ultra-thin wall steel tanks, but sacrificing durability—reducing wall thickness by 0.5mm can potentially reduce the steel tank's lifespan from 15 years to 10 years, leading to higher long-term maintenance costs.

Practical Tips for Choosing a Tank by Need

Selecting a mini scuba tank requires matching the specific scenario: for snorkeling or freediving, choose a 0.5-1L aluminum tank (weighs about 0.9-1.8kg, supports 20-30 minutes of breathing at 10 meters depth); for recreational scuba diving, a 1.5-2L aluminum/stainless steel tank is recommended (1.7L aluminum tank supports about 35 minutes at 10 meters depth, stainless steel models are 10%-15% lighter); technical diving requires a 3L or larger high-pressure tank (300bar pressure, supports long, deep dives). Prioritize checking for DOT-3AL or EN 12245 certification to ensure passing a hydrostatic test every 5 years.

Snorkeling or Freediving

Snorkeling and freediving are lightweight underwater activities close to the surface: snorkelers wear a mask, snorkel, and fins, mainly observing at the surface or in shallow areas of 1-3 meters; freedivers rely on holding their breath to dive, usually not exceeding 10 meters. In this

For snorkeling or freediving, the underwater range is small and the stay time is short, so a small capacity tank of 0.5-1L is sufficient.

First, consider the capacity selection. The most common are 0.5L and 1L aluminum tanks. The 0.5L tank is about 7 cm in diameter and 20 cm high, with an empty weight of 0.9kg, and a total weight of 1.1kg when filled with 200bar compressed air.

This small tank is suitable for beginners or occasional snorkelers: for example, playing at the beach for 1 hour, one refill ashore midway is enough.

In actual underwater use, at 10 meters depth, the gas consumption is about 20 liters per minute (snorkeling breathing frequency is slower than scuba diving). The 0.5L tank (with about 100 liters of usable gas) can sustain 5 minutes.

The 1L tank is slightly larger, 7.5 cm in diameter and 25 cm high, with an empty weight of 1.8kg, and a total filled weight of 2.0kg.

It is suitable for frequent snorkelers or freedivers: at 10 meters depth, about 200 liters of usable gas are available, and at 20 liters/minute consumption, it can sustain 10 minutes.

Freediving enthusiasts use it to assist with practice: for example, diving 5 meters to observe a school of fish, the tank can provide an extra margin of safety if they want to stay longer.

90% of small-capacity tanks on the market are aluminum because aluminum is light, low-cost, and the requirements for corrosion resistance are not high for snorkeling/freediving due to short contact with salt water. Although stainless steel tanks are 10% lighter (1L stainless steel tank empty weight 1.6kg), they are 30% more expensive (1L aluminum tank about ¥500-800, stainless steel models ¥800-1200), which is unnecessary for occasional users.

First, don't buy too cheap uncertified tanks: small tanks also need to have DOT-3AL or EN 12245 certification (with a serial number printed on the body) to ensure they can withstand 200bar pressure and avoid rupture during filling.
Second, regularly check the tank: even if only used a few times, check the inner wall for rust annually (slight oxidation is normal for aluminum tanks, black rust spots should be noted).
Third, use it with a snorkel: the small tank provides auxiliary gas supply. During snorkeling, you mainly rely on the snorkel for breathing, and the tank is more for emergency use.

Beginner Xiao Wang chose a 0.5L aluminum tank for his first snorkeling trip, attached to his waist with a buckle. He played at the beach for 2 hours, refilled once ashore, and didn't feel tired throughout, easily taking underwater photos.

Intermediate player Sister Li often goes freediving in Southeast Asia and chose a 1L stainless steel tank: although more expensive, she dives 3 times a week, and after two years, it hasn't rusted, and the light weight makes fin kicking easier.

Recreational Scuba Diving

Recreational scuba diving is the first choice for most people entering diving: diving to depths of 10-30 meters, viewing coral reefs, and chasing tropical fish, with a single stay of 30-60 minutes.

How much gas is needed

The capacity of a scuba tank for recreational diving is essentially "the total demand for breathing underwater." First, understand two numbers: gas consumption per minute and usable gas volume.

Generally, a beginner's breathing frequency at the surface is 15-20 liters/minute. At 10 meters depth, the pressure doubles, and the consumption will increase to 25-30 liters/minute (because compressed air is compressed when entering the body, which is equivalent to "using more gas"); frequent divers have a more stable breath, potentially reducing it to 20-25 liters/minute.

The "nominal capacity" of a tank is "the volume of gas in an empty tank," for example, a 1.7L aluminum tank has 1.7 liters of compressed air inside when empty, but when filled to 200bar pressure, the actual total gas volume is 1.7×200=340 liters. Usable gas volume needs to be discounted—you cannot use all the gas, as you need to leave 5-10bar residual pressure (to prevent air from sucking back water), so a 1.7L tank actually uses 340×(190/200)=323 liters.

Calculated at 25 liters/minute, the 1.7L tank can sustain 323÷25≈13 minutes?Actually, a simpler method is to use the logic of the "recreational diving tank time calculator": a 1.5L aluminum tank (200bar) can last about 30 minutes at 10 meters depth, 1.7L about 35 minutes, and 2L about 40 minutes (these are common reference values used by dive computers). For example, if you plan to dive for 40 minutes, choosing a 2L tank will be more relaxed, avoiding nervousness due to running out of gas.

How much capacity to choose

The capacity requirements vary greatly with different depths and breathing frequencies.

Shallow area (within 10 meters): For example, coral reef snorkeling + short dives, a 1.5L aluminum tank is sufficient—a beginner using it for 30 minutes will still have 10% gas left, enough to slowly swim back to shore.
Slightly deeper area (15-20 meters): For example, to see the deck of a wreck, the gas consumption will increase to 30 liters/minute. A 1.5L tank can only sustain about 25 minutes (340 liters of usable gas ÷ 30≈11 minutes? No, re-calculate: 1.5L×200bar=300 liters, 285 liters usable, 285÷30≈9.5 minutes? Oh, the previous reference value might be closer to reality. Actually, it's more intuitive to ask the dive shop: "What tank size do you provide for recreational divers?" Most will answer 1.5-2L, as this range covers 90% of shallow diving needs.
People who breathe fast: For example, athletes, or beginners who are easily nervous, their breathing frequency is 30% higher than average. Choosing a 2L tank will last 10-15 minutes longer than a 1.5L tank, avoiding the anxiety of "not enough gas."

How to balance weight

Once the capacity is chosen, weight is the second consideration—after all, every 100 grams lighter makes fin kicking underwater easier.

Aluminum tank: Most common, cheap, slightly heavier. For example, a 1.7L aluminum tank has an empty weight of 1.6kg, and a total weight of about 2.5kg when filled (including 200bar air).
Stainless steel tank: 10%-15% lighter, for example, a 1.7L stainless steel tank has an empty weight of 1.5kg, and a total filled weight of about 2.3kg. More importantly, it has strong corrosion resistance, the inner wall remains bright, suitable for "high-frequency users" who dive 2-3 times a week. But the price is 20%-30% higher: a 1.7L aluminum tank is about ¥800-1200, and a stainless steel model costs ¥1200-1500.

Is it worth paying ¥400 more for 100 grams lighter? Depends on your diving frequency: if you are a beginner who "dives 5 times a year," an aluminum tank is enough; if you are an enthusiast who "dives 4 times a month," the durability and light weight of a stainless steel tank will be worth it.

Pressure, Certification, and Portability

Choose 200bar or 300bar pressure? 200bar is enough for recreational diving—most dive shop compressors can reach 200bar, and a 200bar tank is smaller and less bulky to carry. A 300bar tank is more suitable for technical diving, unnecessary for recreational use, and costs more.
Must check the certification: The tank body must have the DOT-3AL (US standard) or EN 12245 (European standard) serial number printed on it. If buying a used tank, check for the latest 5-year hydrostatic test label (the test pressure is 1.5 times the working pressure, e.g., a 200bar tank should be tested to 300bar). Do not buy if missing, safety first.
Small conveniences in design: For example, choose a tank with a handwheel or screw-on tank valve," and less likely to come loose during diving; the tank body has depth/time labels (e.g., marked "10 meters=35 minutes"), so you don't have to calculate it yourself, making it easier for beginners; there is also a "concave design" tank body.

Beginner vs. Veteran Choices

Beginner Xiao Wu: Chose a 1.5L aluminum tank (¥800) for his first recreational dive. He dived for 28 minutes, with 5% gas remaining, following the instructor to see corals the whole time, and didn't feel tired. He said: "The tank is light, and there's no pressure when strapped into the harness. I'll try the 1.7L next time."
Veteran Sister Chen: Dives 3 times a week, chose a 1.8L stainless steel tank (¥1400).

Technical Diving or Deep Diving

Technical diving or deep diving (e.g., wreck exploration below 30 meters, cave diving, deep sea canyon surveys) differs from recreational diving mainly in "longer duration and higher risk": you might stay underwater for more than 1 hour and need to handle decompression sickness and complex environments (e.g., sharp debris in wrecks). You must choose a large capacity (3L or more), high-pressure (300bar) steel tank to support long-duration breathing and hold the extra gas needed for the decompression phase.

Why recreational dive tanks cannot be used

The limit for recreational diving is generally 30 meters, with gas consumption of about 30 liters/minute; but for technical diving at 40 meters, the pressure quadruples, and gas consumption per minute will increase to 40-50 liters (the body needs more oxygen to fight pressure, breathing is heavier).

Suppose you plan to dive to 40 meters, staying for 60 minutes, plus the decompression phase (staying 3 minutes for every 10 meters, requiring an extra 500 liters of gas), the total gas consumption is approximately: 60 minutes×45 liters/minute + 500 liters = 3200 liters.

The total gas volume of a 2L aluminum tank (200bar) for recreational diving is only 400 liters, not even a fraction of the requirement. A technical dive tank must hold more: for example, a 3L 300bar steel tank has a total gas volume of 3×300=900 liters, which can cover the "basic needs" of most technical dives. For example, two 3L tanks have a total of 1800 liters, which is the minimum before daring to descend.

First, calculate the dive plan

The tank capacity for technical diving is not "guessed," but calculated based on depth, gas consumption, and mission time. Here is a simple formula:

Total Gas Volume Needed = (Dive Time × Underwater Gas Consumption) + Decompression Gas Needed + Redundancy Gas (reserve 10%-15% for backup)

For example:

Diving 50 meters, planned stay 40 minutes, underwater gas consumption 50 liters/minute → 40×50=2000 liters;
Decompression phase: staying 2 minutes for every 5 meters, total needs 300 liters;Redundancy gas: add 200 liters → Total gas needed 2500 liters.

In this case, choose a 3L 300bar steel tank (900 liters per tank), you need to carry 3 tanks (2700 liters); or choose a 4L 300bar tank (1200 liters per tank), 2 tanks are enough (2400 liters, close enough).

There is a default rule among technical divers: the deeper the dive, the capacity must increase by at least 1L, use 3L for 30 meters, and 4L for 50 meters.

Higher is not always better

Many people think "higher pressure means more gas," but for technical diving, 300bar is the "gold standard" for high-pressure tanks.

A 300bar tank balances volume and weight perfectly: for example, a 3L steel tank empty weight 3.2kg, full weight 4.5kg, not too tiring to carry;
For higher pressure like 350bar, the tank body needs to be made thicker, increasing the weight to 4kg, and not all dive shops have equipment that can fill up to 350bar.
Safety-wise, 300bar is the "comfort zone" for steel tanks: DOT-3AL or EN 12245 standards stipulate that a 300bar steel tank must pass a hydrostatic test at 1.5 times the pressure (i.e., 450bar).

Choose steel or aluminum for material

Wrecks have rusty nails, cave walls have sharp stalactites, and seaside diving has salt corrosion—in these cases, steel tanks are more durable than aluminum tanks.

Aluminum tank problems: Prone to deformation under high pressure, for example, hitting a wreck debris might cause a dent, affecting the seal; salt in seawater corrodes the inner wall, and after a few years, black rust spots may appear, which although not affecting safety, reduces the tank's lifespan;
Steel tank advantages: High hardness, a knock will at most chip off some paint, no deformation; better corrosion resistance, the inner wall remains bright even after soaking in the sea for a year; although the weight is 10%-15% heavier than aluminum tanks (3L steel tank empty weight 3.2kg, aluminum tank 2.8kg), technical divers care more about "not breaking."

Don't ignore the details: Valve, Label, and Test

The details of a technical dive tank are more important than capacity:

The valve must be "high-pressure dedicated": For example, a tank valve with a "pressure reducing device"—the gas flow in technical diving is high, and an ordinary valve will "blast air," which can cause choking; a pressure reducing valve can slow down the airflow, making breathing smoother;
Labels must be complete: The tank body must be printed with the DOT-3AL or EN 12245 300bar certification number, and also have the latest 5-year hydrostatic test label (e.g., test date is 2020, next test is due in 2025);
Handle with care: The body of a high-pressure tank is made of "pre-stressed steel," scratching it can reduce the steel's strength. Wear gloves when carrying, and avoid rubbing against rocks or metal; use wide shoulder straps when wearing to disperse the weight and prevent marks on the shoulders.

Technical Diver's Choice

A wreck diver of 10 years, his gear is two 3L 300bar steel tanks, plus a rebreather. He said: "The space inside the wreck is small, and the movements are large. The steel tanks have hit the wall many times, but never deformed; the double tanks hold 1800 liters of gas, enough for a 40-meter dive, staying for 60 minutes, plus decompression."

Beginner technical diver Xiao Li chose a 4L 300bar steel tank for his first 30-meter cave dive. His instructor calculated for him: total gas needed is about 2000 liters, the 4L tank has 1200 liters, plus the rebreather, which is enough to complete the dive.