How long does my scuba tank last? This is probably the most frequently asked question our instructors get from new divers. And the answer is always the same: “It depends…”. But what factors does it depend on, and how can I conserve air?
Here are three factors that influence how long you can breathe underwater, along with a few tips that might help you squeeze a few extra minutes out of your dives.
1. The tank size
When you walk through the Scubanana Dive Center, you’ll see a wide range of tanks in different sizes and shapes. The most commonly used tanks for beginner divers at our dive center are steel tanks with a capacity of 12 L or 15 L. A full scuba tank typically has a pressure of 200 bar. So:
- 12 L tank at 200 bar → approx. 2400 L of air
- 15 L tank at 200 bar → approx. 3000 L of air
n short: the larger the volume, the longer the air lasts.
2. The dive depth
Attention: it’s about to get a bit more technical. The deeper we dive, the higher the ambient pressure. The higher the ambient pressure, the more compressed our breathing gas is—and the higher our air consumption.
Let’s take a closer look at this:
At the surface at sea level, we have 1 bar of ambient pressure. For every 10 meters of depth in saltwater, an additional 1 bar is added. So if we dive to -10 m, we already have 2 bar of ambient pressure. This compresses our breathing gas to half its volume, and our air consumption is twice as high as at the surface.
At -20 m, we already have 3 bar of ambient pressure, and our consumption is three times higher than at the surface.
| Depth | Ambient pressure | Relative air consumption |
| 0 m | 1 bar | x1 |
| -10 m | 2 bar | x2 |
| -20 m | 3 bar | x3 |
| -30 m | 4 bar | x4 |
So we remember: the deeper the dive, the higher our air consumption. During a trial dive at Scubanana, you’ll typically dive between -5 m and -12 m. At -5 m, your consumption would be about 1.5 times higher than at the surface, and at -12 m about 2.2 times higher.
By comparison, an advanced diver is allowed to dive to depths of up to -30 m. At that depth, air consumption is already four times higher than at the surface.
3. Your breathing
The most obvious factor determining how long your breathing gas lasts is your own breathing. Both the depth of your breaths and your breathing rate play a major role.
New divers, for example, may be nervous and haven’t yet developed solid diving techniques. This can quickly lead to a high SAC (Surface Air Consumption) of over 20–30 L/min. Your Scubanana instructor, on the other hand—who spends more time underwater than above it, has excellent buoyancy and fin control, and moves in a relaxed, effortless way—likely has a SAC of only 10–12 L/min.
Here’s an example:
During a trial dive at -10 m, we typically use 12 L tanks with 200 bar pressure. Of that, 50 bar is our reserve, so we only plan to breathe down 150 bar before returning to the surface. That gives us:
12 L tank with 150 bar → approx. 1800 L of air available to use
We’ve learned that at -10 m our air consumption is twice as high as at the surface, so we need to multiply our SAC by 2.
- 1800 L of available gas / (12 L/min × 2 bar ambient pressure) = 75 min
- 1800 L of available gas / (25 L/min × 2 bar ambient pressure) = 36 min
If our consumption is 12 L/min, we could dive for up to 75 minutes. A diver with a higher air consumption of 25 L/min, on the other hand, would reach their reserve after just 36 minutes.
In addition to our experience, there are many other factors that can affect our SAC, such as currents, waves, equipment, temperature, and more.
In addition, people with greater body mass or more muscle mass generally have a higher basal metabolic rate and require more oxygen at rest. As a result, they often consume more air than smaller divers, even when diving calmly. Women therefore often have an advantage over men due to having less muscle mass.
How can I extend my dive time?
But setting all the calculations aside—here are a few tips to help you improve your air consumption:
- Practice, practice, practice…
The more time you spend underwater, the more comfortable you’ll feel—and your air consumption will improve naturally.
- Focused buoyancy training
The better your trim in the water and the more controlled your fin kicks are, the lower your air consumption will be. Proper buoyancy control ensures that you move efficiently through the water without unnecessary effort. If you want to specifically improve your buoyancy, you can take courses such as the PADI “Peak Performance Buoyancy” specialty. Also, make sure to configure your equipment as streamlined as possible. This not only protects your gear but also reduces drag and helps you conserve air.
Slow, steady breathing significantly reduces air consumption. Rapid or erratic breathing causes you to use more air than necessary. Ideally, you should aim for deep, calm breaths.
IMPORTANT: Never hold your breath underwater, as this can lead to serious lung injuries.
- Improve your physical fitness
Good baseline fitness reduces oxygen demand during physical activity. Divers with better endurance typically consume less air underwater.
In short: the key to lower air consumption is calm, controlled, and efficient diving—combined with good buoyancy, relaxed breathing, and sufficient experience.
Also: the deeper we dive, the shorter our dives become. Aside from “better diving,” the only real solution is a larger tank.
