What is the formula used?

Duration (minutes) = (gauge pressure in PSI − reserve pressure in PSI) × cylinder factor in L/PSI ÷ continuous flow in L/min. For example, an E factor of 0.28, 2,000 PSI, 200 PSI reserve and 10 LPM gives 50.4 minutes.

Should I enter gauge pressure or absolute pressure?

Enter gauge pressure — the reading shown on the cylinder regulator gauge. A reading of zero means there is no pressure above atmosphere available to drive delivery.

What cylinder factor should I use?

Common teaching factors include D 0.16, E 0.28, M 1.56, G 2.41 and H/K 3.14 L/PSI. Names, capacities and rated pressures vary by country and supplier, so the cylinder or supplier value takes priority.

Why does the result differ from manufacturer charts?

Charts may assume a different rated capacity, factor, reserve, regulator behavior or full starting pressure. This page uses exactly the current pressure, reserve, factor and continuous flow that you enter.

How long does an E cylinder last at 2 LPM?

With the common factor 0.28 L/PSI, a cylinder at 2,000 PSI with a 200 PSI reserve holds (2,000 − 200) × 0.28 = 504 L, which lasts 252 minutes (4 h 12 min) at 2 LPM, 126 minutes at 4 LPM and about 50 minutes at 10 LPM.

How long does a D cylinder last?

With the factor 0.16 L/PSI, 2,000 PSI and a 200 PSI reserve give 288 L: 144 minutes (2 h 24 min) at 2 LPM, 72 minutes at 4 LPM and about 29 minutes at 10 LPM.

How do I find the cylinder factor for my tank?

Divide the cylinder’s full capacity in liters by its full (service) pressure in PSI. For example, a 680 L cylinder filled to 2,200 PSI has a factor of about 0.31 L/PSI. Teaching factors are D 0.16, E 0.28, M 1.56, G 2.41 and H/K 3.14.

How long does liquid oxygen last?

One liter of liquid oxygen expands to about 860 L of gas, and respiratory-care references use about 344 L of gas per pound of liquid. A portable holding 1.2 L of liquid gives about 1,032 L of gas, or 516 minutes (8.6 h) at 2 LPM, before evaporation losses. Liquid also evaporates when not in use.

How many oxygen tanks do I need for a trip?

Divide the oxygen needed (trip minutes × LPM) by the usable liters in one full cylinder (full PSI − reserve) × factor, and round up. A 6-hour trip at 2 LPM needs 720 L, so 2 full E cylinders (504 L each at 2,000 PSI with a 200 PSI reserve). Carry extra for delays.

Does a pulse-dose conserver make a tank last longer?

Yes. Conservers deliver oxygen only at the start of each breath, so a tank lasts several times longer than on continuous flow; how much longer depends on the device, its setting and the breathing rate. Use the manufacturer’s duration chart for the conserver; this page’s main formula is for continuous flow.

What reserve pressure should I use?

The default 200 PSI is a common teaching value, not a universal instruction. Use the reserve required by your facility, transport service, regulator, manufacturer and applicable protocol.

Can I use this for a conserving device or ventilator?

The simple formula assumes continuous flow. Pulse-dose conservers, ventilators, leaks, regulator losses and variable demand require device-specific consumption data and a larger operational margin.

Oxygen Tank Duration Calculator

Minutes = (gauge PSI − reserve PSI) × cylinder factor ÷ LPM. An E cylinder (0.28) at 2,000 PSI with a 200 PSI reserve lasts 252 minutes (4 h 12 min) at 2 LPM. Liquid oxygen: liters of liquid × 860 ÷ LPM.

Cylinder Parameters

Oxygen Supply

Current Tank Pressure (PSI gauge)

Reading shown on the regulator gauge.

Example Full Pressure (PSI gauge)

Used only for the fill bar; enter the supplier or cylinder-label value.

Cylinder Factor (L/PSI)

E is commonly 0.28; confirm the value for the actual cylinder.

Factor from label capacity

Capacity (L)

Full pressure (PSI)

Safe Residual Pressure (PSI)

Use the reserve required by your local protocol.

Flow Rate (liters per minute)

Prescribed or set delivery rate in LPM.

Trip or Outing Length (hours, optional)

Counts full cylinders of the selected size needed at this flow.

Quick Cylinder Presets

Enter cylinder parameters and click Calculate Duration.

Estimated Duration

—

Trip Planner

Available O₂

—

liters at atmospheric pressure

Total Duration

—

minutes

Tank Fill Level

—

Pressure percentage relative to the selected preset's example full pressure; verify the actual rated pressure.

Duration by Continuous Flow

Comparison only—do not change a prescribed flow to extend cylinder time.

Flow	Estimated duration	Minutes

Calculation Detail

Oxygen Cylinder Duration Chart

Continuous flow from a full cylinder down to a 200 PSI reserve: minutes = (full PSI − 200) × factor ÷ LPM. M6 and M9 factors are approximate (label capacity ÷ 2,015 PSI); use your cylinder’s label.

Cylinder	Factor (L/PSI)	Full PSI	Usable O₂	1 LPM	2 LPM	4 LPM	10 LPM
D	0.16	2,000	288 L	4 h 48 min	2 h 24 min	1 h 12 min	0 h 29 min
E	0.28	2,000	504 L	8 h 24 min	4 h 12 min	2 h 06 min	0 h 50 min
M6 (≈)	0.08	2,015	145 L	2 h 25 min	1 h 13 min	0 h 36 min	0 h 15 min
M9 (≈)	0.13	2,015	236 L	3 h 56 min	1 h 58 min	0 h 59 min	0 h 24 min
M	1.56	2,000	2,808 L	46 h 48 min	23 h 24 min	11 h 42 min	4 h 41 min
G	2.41	2,000	4,338 L	72 h 18 min	36 h 09 min	18 h 05 min	7 h 14 min
H/K	3.14	2,200	6,280 L	104 h 40 min	52 h 20 min	26 h 10 min	10 h 28 min

Worked example: an E cylinder reads 1,500 PSI, the reserve is 200 PSI and the flow is 3 LPM. (1,500 − 200) × 0.28 = 364 L ÷ 3 LPM = 121 minutes, so it reaches the reserve in about 2 hours. A 6-hour trip at 3 LPM needs 1,080 L, or 3 full E cylinders (504 L each).

Liquid oxygen: minutes = liters of liquid × 860 ÷ LPM (or pounds × 344 ÷ LPM). A stationary reservoir also loses some liquid to evaporation every day, so the real supply runs out sooner than the calculated value.

Planning estimate—not medical advice

This tool does not give medical advice. Use the flow your prescriber or protocol sets, and never lower a prescribed flow to stretch a tank.

Confirm the cylinder identity, factor, gauge, regulator and reserve locally. Actual duration can be shorter because of leaks, variable demand and device behavior. Do not delay clinically required oxygen based on this estimate. Formula and factor context: PAHO inter-hospital transport guidance; liquid oxygen expansion (about 860 L of gas per liter): BOC liquid oxygen equipment guide.

Summary

This calculator estimates continuous-flow duration for a compressed medical oxygen cylinder or a liquid oxygen (LOX) reservoir. For cylinders it subtracts a configurable safe residual pressure from the gauge reading, multiplies by the cylinder factor (liters per PSI) and divides by flow in liters per minute; for liquid oxygen it converts liquid volume (860 L of gas per liter) or weight (about 344 L of gas per pound) to gas and divides by flow. It also shows the clock time the reserve is reached, a full-cylinder duration chart and how many full cylinders a trip needs. Cylinder letters and factors are not universal, so confirm the label, supplier data and local clinical policy. Not medical advice.

How it works

Choose compressed cylinder or liquid oxygen.
Cylinder: enter the gauge pressure in PSI and pick a cylinder preset or enter its factor (label capacity in liters ÷ full pressure in PSI).
Liquid oxygen: enter the liquid amount in liters or pounds; 1 L of liquid gives about 860 L of gas.
Enter the reserve pressure required by your service or facility.
Enter the oxygen flow rate in liters per minute (LPM).
The calculator subtracts reserve pressure, multiplies by the factor and divides by flow, then adds the run-out clock time.
Enter trip hours to see how many full cylinders of the selected size cover the trip at that flow.

Use cases

Estimate continuous-flow supply time using a prescribed or already-set flow.
Plan compressed medical oxygen reserves for EMS transport.
Verify whether a cylinder estimate covers a planned patient transfer plus the locally required margin.
Compare how different continuous-flow settings change estimated duration.
Support hospital cylinder inventory and rotation planning.
Practice respiratory-care cylinder-duration calculations.

Frequently Asked Questions

Last updated: 2026-10-09 · Reviewed by Nham Vu