Oxygen Duration Calculator

Supplemental oxygen duration comes down to how much oxygen you have divided by how fast you're using it, but both sides of that equation shift with altitude. This calculator steps flow rate per person through altitude bands — roughly 1.0 liter per minute (LPM) up to 10,000 ft, rising to 1.5 LPM through 15,000 ft, 2.0 through 18,000 ft, 2.5 through 25,000 ft, 3.0 through 30,000 ft, and 3.5 LPM above that — reflecting the thinner air's lower oxygen partial pressure at higher altitudes. A demand or conserving regulator, which only delivers oxygen on inhalation rather than continuously, cuts that flow rate roughly in half compared to a continuous-flow cannula setup, and total flow scales linearly with the number of occupants sharing the same bottle.

On the supply side, bottle volume (in cubic feet) is converted to liters at 28.3168 L per cubic foot and scaled by what fraction of a full charge the current pressure gauge reading represents, since a half-full bottle only holds half its rated oxygen regardless of its physical size. Duration is simply available liters divided by total flow rate. The calculator also flags the FAR 91.211 threshold that applies at your entered altitude — continuous crew use required above 12,500 ft after 30 minutes, mandatory for all occupants above 14,000 ft, and required for everyone above FL250 — but always build in a real reserve margin beyond the raw duration number, since gauge readings, connector leaks, and cabin altitude assumptions all introduce real-world variance this formula can't see.