**How To Calculate How Long An Oxygen Tank Will Last**. For example, letâ€™s say you have an e cylinder with a pressure of 2200 psi and a flow rate of 2 l/min. Approx length 25 d cylinder:

At a flow rate of 1 liter. Duration of flow = oxygen tank conversion factor *. The formula is a mixture of tank pressure minus residual pressure and cylinder constant.