What This Oxygen Tank Duration Calculator Does
This tool estimates how long an oxygen cylinder may last at a selected continuous flow rate. It is useful for learning the relationship between pressure, cylinder size, usable oxygen volume, and flow.
PSIG Cylinder-Factor Method
For common medical-style oxygen cylinder calculations, the cylinder factor gives the approximate liters available per psi.
Duration = usable oxygen / flow rate
The reserve pressure is subtracted before calculating duration. This avoids planning the cylinder all the way down to zero.
Metric Water-Capacity Method
For metric cylinders, a simple ideal estimate uses water capacity and gauge pressure in bar.
For example, a 5 L cylinder at 150 bar with a 10 bar reserve has approximately:
usable pressure = 150 − 10 = 140 bar free oxygen ≈ 5 × 140 = 700 L
Why Flow Rate Matters
Flow rate is the oxygen delivery rate in liters per minute. Higher flow rates empty the cylinder faster.
| Usable oxygen | Flow rate | Estimated duration |
|---|---|---|
| 500 L | 1 L/min | 500 min |
| 500 L | 5 L/min | 100 min |
| 500 L | 10 L/min | 50 min |
Why This Is Not a Medical Calculator
Oxygen therapy flow rates are clinical settings and should be set by qualified healthcare professionals. This calculator only performs arithmetic. It does not know the patient, device type, oxygen prescription, regulator behavior, or emergency context.
Why This Is Not a Scuba Calculator
Scuba gas planning is different because breathing gas consumption increases with ambient pressure at depth. Dive planning also needs reserve rules, ascent gas, buddy/team gas, decompression planning, gas mix limits, and training-specific procedures.
Example Calculation
Suppose an E cylinder has 2000 psig, a 200 psig reserve, a cylinder factor of 0.28 L/psi, and a flow of 2 L/min.
usable pressure = 2000 − 200 = 1800 psi usable oxygen = 1800 × 0.28 = 504 L duration = 504 / 2 = 252 min
With a 20% safety margin:
planned duration = 252 × (1 − 0.20) planned duration = 201.6 min
Common Mistakes
- Forgetting to subtract reserve pressure.
- Using bar with a PSIG cylinder factor.
- Using tank water capacity as if it were stored gas volume.
- Ignoring regulator, gauge, and device-specific behavior.
- Using a surface-duration calculator for diving.
- Using an arithmetic estimate for medical or emergency decisions.
Frequently Asked Questions
What is a cylinder factor?
A cylinder factor estimates how many liters of oxygen are available per psi of pressure for a given cylinder size.
Why is reserve pressure included?
Reserve pressure is a safety allowance. It keeps the calculation from assuming the cylinder can be used all the way to zero pressure.
Can I use bar instead of psi?
Yes. Use the metric method and enter cylinder water capacity in liters, current pressure in bar, and reserve pressure in bar.
Can I use this for medical oxygen planning?
No. It is an educational estimate only. Medical oxygen decisions require qualified clinical guidance and equipment-specific instructions.
Can I use this for scuba gas planning?
No. Scuba gas planning requires depth, ambient pressure, reserve strategy, breathing gas mix, training rules, and dive-specific calculations.