Gas Cylinder Contents Calculator

Gas Cylinder Contents Calculator

"How much gas is actually left in this cylinder?" has a precise answer for gases stored purely as compressed gas (not liquefied) - the ideal gas law solved directly for mass.

The Formula

n = PV / RT, then mass = n × M

Worked Example

A 50L nitrogen cylinder at 15,000 kPa (about 150 bar) and 293K: n = (15,000 × 50)/(8.314 × 293) ≈ 307.9 mol, mass = 307.9 × 28.01 ÷ 1000 ≈ 8.62 kg remaining.

How to Use This Calculator

1. Enter the cylinder pressure gauge reading.
2. Enter the cylinder's internal volume.
3. Enter gas temperature and molar mass.

Important limitation: this works well for gases that remain far from their liquefaction point at cylinder pressure, like nitrogen, oxygen, or compressed air. For gases stored as a liquid-vapor mixture (like propane or CO2), pressure alone does not reliably indicate remaining quantity, since pressure stays roughly constant until the liquid is nearly exhausted - a scale (weighing the cylinder) is the reliable method for those gases instead.