Oxygen Tank Duration Calculator
Minutes of oxygen from cylinder size, pressure, reserve, and flow rate.
What it does
Oxygen transports run on arithmetic as much as on lungs. A cylinder holds a fixed gas volume at its pressure, the flowmeter spends it by the minute, and the trip consumes both plus waiting time. Dividing wrong strands a patient in an elevator with an empty tank.
The tool above does the cylinder math: minutes from pressure, reserve, factor, and flow. Pick the tank letter, enter gauge and reserve pressure with flow. It returns minutes, hours, and liters aboard. Defaults of an E cylinder at 1500 psi with 200 reserve at 2 L/min open solved at 182 min.
Tank factors convert pressure to liters: E at 0.28 is the transport standard, D at 0.16 suits short trips, and H at 3.14 feeds high flows for hours. A full E near 2000 psi at 10 L/min holds under an hour, which surprises teams used to wall oxygen.
Reserve discipline separates planning from hoping. Regulators read imprecisely near zero and flow sags, so transports plan to 200 or even 500 psi and swap early. The worked case keeps 200 back, turning 420 theoretical liters into 364 usable ones.
Use the table to feel sizes and flows, then run the transport. Add imaging delays and the return trip before choosing tanks, and verify gauge and flow at the bedside.
How to use
- Pick the cylinder letter.
- Enter gauge pressure in psi.
- Enter reserve pressure, often 200.
- Enter flow in L per min.
- Read minutes first, then hours and liters.
- Carry a spare when the trip nears the answer.
Formula
- psi
- Gauge pressure in psi.
- Reserve
- Unplanned reserve kept back, often 200 psi.
- Factor
- Cylinder factor in L per psi.
- Flow
- Delivery setting in L per min.
Boyle's law in work clothes: pressure times the cylinder factor estimates liters aboard. Factors in L per psi: D 0.16, E 0.28, M 1.56, G 2.41, H and K 3.14. Subtract the safe reserve first; planning to zero is never acceptable practice.
Worked example
Example: E cylinder, 1500 psi, 2 L/min
An E cylinder reads 1500 psi with a 200 psi reserve at 2 L/min. How long does it last?
- Usable pressure: 1500 - 200 = 1300 psi.
- Gas volume: 1300 x 0.28 = 364 L.
- Minutes: 364 / 2 = 182 min.
- Hours: 182 min is 3 h 02 min.
- Plan the trip plus elevator waits inside 182 min.
- Change the cylinder at reserve, never at zero.
Reference table
| Cylinder | Factor | Worked trip |
|---|---|---|
| D | 0.16 L/psi | 1800 psi, 200 reserve, 4 L/min: 64 min |
| E (worked) | 0.28 L/psi | 1500 psi, 200 reserve, 2 L/min: 182 min |
| M | 1.56 L/psi | Full M near 3450 psi feeds days at 2 L/min |
| H or K | 3.14 L/psi | 2000 psi, 200 reserve, 10 L/min: 565 min |
Limits
- Planning estimate, not bedside orders.
- Gauge error grows near empty.
- Temperature swings move readings.
- Leaks and flushing waste uncounted gas.
Common mistakes
- Planning to zero instead of reserve.
- Using the wrong tank factor.
- Forgetting the return trip and delays.
- Reading flow in the wrong units.
- Trusting one gauge without a spare.
Try it yourself
Quick checks. Answers sit tucked under each question.
D cylinder at 1800 psi, 200 reserve, 4 L/min?
(1800 - 200) x 0.16 = 256 L. At 4 L/min that is 64 min, about 1 h 04 min.
H cylinder at 2000 psi, 200 reserve, 10 L/min?
(2000 - 200) x 3.14 = 5652 L. At 10 L/min that is 565 min, about 9 h 25 min.
Gauge already at reserve?
Zero usable pressure means zero minutes. Fill or swap before any trip.
Questions
What are the tank factors?
0.28 L per psi for E, 0.16 for D, 1.56 for M, 2.41 for G, 3.14 for H and K. Multiply gauge by the factor for liters.
What is safe residual pressure?
The pressure kept unplanned so flow never falters: 200 psi is common, 500 on high flow transports. Subtract it before dividing.
How long does a D cylinder last?
(1800 - 200) x 0.16 / 4 = 256 / 4 = 64 min, about 1 h 04 min. Small tanks drain fast.
And an H cylinder at 10 L/min?
(2000 - 200) x 3.14 / 10 = 5652 / 10 = 565 min, about 9 h 25 min. Big tanks feed high flows for hours.
Why not run to zero?
Regulators read poorly near zero and flow sags. Plan with reserve and carry a full spare on every transport.
Can I use this for a real patient?
No. This page estimates gas math for planning and study. Bedside care follows orders, protocols, and live gauge checks.
Sources
- Cornell Weill: oxygen tank duration, Boyle's law factors
- Virginia Dept. of Health: oxygen cylinder guidance and factors