# Gas Cylinder Contents Calculator

URL: https://hifreetools.com/gas/cylinder

> Enter the gas, the cylinder size (water capacity) and the pressure on the gauge to see how much gas you can draw, in Nm³, litres, scf and kilograms. Add your consumption to see how long it will last. It uses the real-gas density from CoolProp, because at 200–300 bar the simple P·V estimate is 5–14% off.

## Quick answer

A 50 L nitrogen cylinder at 200 bar (gauge) and 15 °C holds about 8.92 Nm³ (9.41 m³ at 15 °C), or 11.15 kg, that can be drawn down to atmospheric pressure. Contents = cylinder volume × (gas density at the gauge pressure − density at the end pressure); oxygen in the same cylinder holds 10.05 Nm³ because it compresses more easily.

## Formula

- contents (kg) = V × (ρ(T, P_full) − ρ(T, P_end)) Nm³ = kg / ρ_N runtime = contents / consumption

## Examples

- 50 L nitrogen cylinder at 200 bar: Nitrogen, 50 L, 200 bar gauge, 15 °C, empty to 0 bar → 8.92 Nm³ (9.41 m³ at 15 °C) = 11.15 kg; Z = 1.0485
- Same cylinder at 300 bar: Nitrogen, 50 L, 300 bar gauge, 15 °C → 12.32 Nm³ = 15.39 kg (not 14.0 Nm³)
- Medical/industrial oxygen, 10 L at 150 bar: Oxygen, 10 L, 150 bar gauge, 20 °C → 1.47 Nm³ (1,555 L at 15 °C) = 2.10 kg
- Runtime of a bundle: 12 × 50 L argon at 200 bar, 15 °C, consumption 20 Nm³/h → 119.86 Nm³ in total; lasts about 6 h 0 min

## FAQ

**How much gas is in a 50 litre cylinder at 200 bar?**
For nitrogen about 8.9 Nm³ (9.4 m³ at 15 °C); oxygen about 10.0 Nm³; argon about 10.0 Nm³; helium 8.5 Nm³ and hydrogen 8.3 Nm³. The differences come from how each gas departs from ideal behaviour at high pressure.

**Why isn't it simply 50 L × 200 = 10,000 litres?**
Two reasons. Gas at 200 bar is not ideal: nitrogen, hydrogen and helium compress less (Z > 1), oxygen and argon more (Z < 1). And the litres are usually quoted at 15 °C or 0 °C, not at the cylinder temperature. The calculator shows the size of the error for your cylinder.

**How long will my cylinder last?**
Open More options and enter your consumption in L/min, Nm³/h, scfh or kg/h. The runtime is the usable contents divided by that rate, for example a 10 L oxygen cylinder at 150 bar lasts about 13 hours at 2 L/min.

**Can I use this for a CO₂ or propane cylinder?**
Not by pressure. CO₂ and propane are liquid in the cylinder, and the gauge shows only the vapour pressure until nearly empty. Weigh the cylinder: contents = current weight − tare weight stamped on the cylinder (the weighing option does this).

**What is water capacity?**
The internal volume of the cylinder, stamped on it in litres (e.g. 50 L) or as water weight. It is the size of the container, not the amount of gas.

**Should I use gauge or absolute pressure?**
Enter what your gauge reads and keep the unit on bar (gauge) or psi (gauge). The calculator adds 1 atm to get the absolute pressure the physics needs.


## Sources

- [CoolProp 8.0.0 — open-source thermophysical property library (Bell et al.)](https://coolprop.org/)
- [NIST Chemistry WebBook — Thermophysical Properties of Fluid Systems](https://webbook.nist.gov/chemistry/fluid/)
- [EIGA — European Industrial Gases Association, gas cylinder safety](https://www.eiga.eu/)
- [Compressed Gas Association (CGA) — industrial gas standards](https://www.cganet.com/)

Runs in the browser; nothing is uploaded. Cite as: HIFreeTools, "Gas Cylinder Contents Calculator", https://hifreetools.com/gas/cylinder