Air Consumption Ratio

Once you know how much air you breathe in a one-minute period, it is possible to calculate how long a dive you can complete. You can also see on a minute-by-minute basis the strong effects of pressure on the air consumption ratio.

1. Starting pressure – ending pressure = total air consumption (by pressure)
2. Air consumption pressure x tank volume = total air consumption (by volume)
3. Total air consumption (by volume) ÷ diving time (by minutes)
   = total air consumption (by volume)/minute
4. Total air consumption (by volume)/minute ÷ average depth pressure
   = air consumption ratio

Practical Dive Time

Since we are limited to our tank’s capacity, our dive time is also limited. It is important to calculate your air consumption ratio, since it varies widely - advanced divers’ air consumption ratio is about 20L/minute, while beginners average about 40L/minute.

Remember, we leave 50 bar reserve in our tank at exiting for safety. As a rule, you should use the following for calculating your air consumption ratio.
We use litre (L) for tank volume; and we use bar to denote pressure.

Practical Dive Time Calculation

Volume capacity of tank usedx(starting tank pressure - 50)÷40÷maximum depth