Oxygen Tank Duration Calculator: How Long Will My Oxygen Cylinder Last?
Find how many minutes or hours an oxygen tank will last from its size (D, E, M, G, H/K, rated litres or water volume), gauge pressure in psi or bar and flow rate in L/min.
How it works
Duration (min) = (gauge pressure − safe residual pressure) × cylinder factor ÷ flow (L/min) · cylinder factor (L/psi): D 0.16, E 0.28, M 1.56, G 2.41, H/K 3.14 · factor = full content (L) ÷ full pressure (psi) · metric cylinders: duration = water volume (L) × (pressure − reserve) in bar ÷ flow
An oxygen cylinder holds a fixed amount of gas per unit of pressure, so the gauge pressure tells you how much oxygen is left. The cylinder (tank) factor converts psi into litres: an E cylinder holds about 0.28 L for every psi. Subtract a safe residual pressure, usually 200 psi, because a cylinder should be changed before it runs dry, multiply by the factor to get usable litres, and divide by the flow rate in litres per minute. If your cylinder has no letter size, choose “Rated capacity” and enter the content printed on the label with its full pressure, or “Water volume” for European and Latin American cylinders labelled in litres and bar (a 10 L cylinder at 200 bar holds about 2,000 L). Pressures can be entered in psi, bar or kPa. Tables show how long the cylinder lasts at other flow rates and how the other cylinder sizes compare. A pulse-dose conserver stretches the supply by roughly the savings ratio its maker states. The Oxygen Content calculator works on oxygen carried in the blood; this one is about the gas supply.
Worked example
An E cylinder reads 2,000 psi and the patient needs 2 L/min by nasal cannula. Keeping a 200 psi reserve leaves 2,000 − 200 = 1,800 psi. With the E factor of 0.28 L/psi that is 1,800 × 0.28 = 504 L of oxygen, and 504 ÷ 2 = 252 minutes, so the cylinder needs changing in about 4 h 12 min. Run to empty it would last 2,000 × 0.28 ÷ 2 = 280 min (4 h 40 min). At 15 L/min the same cylinder lasts only 33 minutes.
Sources: ProTrainings: How long does an oxygen cylinder last? (formula, 200 psi reserve, cylinder constants, D cylinder example) · Omni Calculator: Oxygen tank duration (D and E cylinder examples)
Frequently asked questions
How long does an E oxygen tank last?
A full E cylinder (about 2,000 psi, 680 L) lasts roughly 4 h 12 min at 2 L/min, 2 h 48 min at 3 L/min and 33 minutes at 15 L/min, keeping a 200 psi reserve. At 1 L/min it lasts about 8 h 24 min.
What is the oxygen tank duration formula?
Minutes = (gauge pressure in psi − 200 psi) × tank factor ÷ flow in L/min. The tank factor is 0.16 for D, 0.28 for E, 1.56 for M, 2.41 for G and 3.14 for H or K cylinders. For a D cylinder at 2,000 psi and 15 L/min: (2,000 − 200) × 0.16 ÷ 15 = 19.2, about 19 minutes.
Why subtract 200 psi?
The 200 psi safe residual keeps a little pressure in the cylinder so air and moisture cannot get in and so you are never caught with an empty tank. Change or refill the cylinder when the gauge reaches about 200 psi (14 bar).
How do I calculate duration with a cylinder in bar and litres?
Multiply the water volume by the usable pressure in bar to get litres of oxygen, then divide by the flow. A 10 L cylinder at 150 bar with a 10 bar reserve holds about 10 × 140 = 1,400 L, which lasts 700 minutes (11 h 40 min) at 2 L/min.
How long does an oxygen concentrator or portable tank last?
A concentrator makes oxygen from room air and runs as long as it has power. Small portable cylinders such as D and M6 last from under an hour to a few hours depending on flow; a pulse-dose conserver can make them last 2–4 times longer.
Related calculators
Planning estimate only. Follow your oxygen prescription, your supplier’s cylinder data and local EMS or hospital protocols; never change the prescribed flow to make oxygen last longer, and always carry a spare supply on journeys.