Calculating oxygen capacity of cylinder and it’s lifespan

Supplementing oxygen through the oxygen cylinder either to thrive in extreme altitudes (>8,000 meters) to ascent peak or to treat hypoxia related illnesses is a very common practice. This has been in practice since decades. But, every time someone decides to use the oxygen cylinder, s/he faces the most difficult questions;

  1. How much oxygen is there in the cylinder? And,
  2. How long will it last?

Cylinder size and total oxygen capacity:

The oxygen capacity of the cylinder depends on the size of the cylinder and here is the common type of cylinder size and its capacity:

Cylinder sizeDEFGJ
Oxygen capacity (Liters)340680136034006800
Water capacity (Liters)2.3L4.7L17L39L47.2L

To calculate the oxygen capacity of any type of oxygen cylinder the formula is:

Cylinder Capacity (Liters) = Water capacity × 144

Longevity of the cylinder/Duration of oxygen supply:

              This depends on the flow rate, cylinder (tank) pressure, residual pressure and conversion factor of different cylinder size. And, this can be calculated using the following formula:

Time to runout a cylinder = (Cylinder pressure in PSI – 200) × Cylinder conversion factor ÷ Flow rate (Liter/min)

Residual pressure = 200 (constant)

Cylinder pressure = measured in the pressure gauze attached to the cylinder

Flow rate = desired flow rate adjusted in the flow meter

Cylinder sizeCylinder conversion factor

Cylinder conversion factor = depends on size of cylinder


Please calculate the time to rundown the oxygen cylinder (F-size) at given pressure and flow rate:

Gauze pressure = 2,000 psi

Residual pressure = 200 psi

Flow rate = 5 liter/min

Time duration = (2000-200) × 0.68 ÷ 5  

                      = 244.8 minutes or 4.08 hours

Safely used the oxygen delivery devices!

Dr. Santosh Baniya, MD (July, 2022)