Airway & Oxygen

Oxygen Cylinder Duration Calculator

How long a cylinder will last at a given flow.

Reviewed by Alex G, BSN, RN, CEN, CCRN, CMC, NREMT-P · From the Reference tab of the app

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Formula

Minutes = (gauge psi − 200 safe residual) × cylinder constant ÷ flow (L/min)

How it is used

• Constants: D 0.16, E 0.28, M 1.56, G 2.41, H/K 3.14 L per psi.
• A full D cylinder (about 2,000 psi) lasts under 20 minutes at 15 L/min; switch to the onboard supply for transport and carry a spare on long calls.

Same formula as the app. Open it in the web app.

Related one-pagers

• EMT: Airway, Oxygen and Equipment ChecksDuration in minutes = usable pressure × cylinder constant ÷ flow, where usable pressure is the gauge reading minus the safe residual. RT Zone lists D 0.16, E 0.28, M 1.36 and H 3.14 L/psig, notes a full cylinder holds about 2,000–2,200 psig and suggests changing near 500 psig. ProTrainings (a UK oxygen course page) and Omni Calculator list M as 1.56, and ProTrainings subtracts a 200 psi residual, which is also what EMT texts and exam items use; the two sources differ, so use whatever constant and residual the protocol or question gives. Examples: D at 1,800 psi, 2 L/min: (1,800 − 200) × 0.16 ÷ 2 = 128 min. M at 2,000 psi, two masks at 15 L/min: 1,800 × 1.56 ÷ 30 ≈ 94 min, short of a 100-minute trip. D at 1,000 psi, 15 L/min: 800 × 0.16 ÷ 15 ≈ 8.5 min, so switch to onboard oxygen before leaving. Common errors: forgetting the residual, the second patient's flow or the right constant. Turning a non-rebreather down to stretch a cylinder trades a supply problem for hypoxemia.
• Airway and RSI

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For education and exam preparation only. Follow your institution’s protocols. For education and exam preparation only. Verify results independently and follow your local protocols and medical direction. Not a substitute for clinical judgment.