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Gas Management

Cylinder Capacity Calculator

Convert water volume and free-gas capacity using the conventional ideal-gas estimate at 1 bar. Actual cylinder inventory depends on gas properties and temperature.

Cylinder
A metric label gives the internal water volume; an imperial label gives the free gas the cylinder holds at its working pressure. Pick which one you are entering and get the other.
Common cylinders
L

Allowed range: 0.1 to 100 L.

bar

Allowed range: 1 to 400 bar.

Cylinder in both unit systems
Water volume
12.0 L (0.42 cu ft)
Rated gas capacity
2400 L (84.8 cu ft)
Working pressure
200 bar (2901 psi)

Conventional ideal-gas estimate = water volume × gauge working pressure, expressed as free gas at 1 bar at the same temperature. This is not measured gas inventory. Real-gas effects can make the available gas materially different, especially at high pressure. Use the manufacturer's capacity rating when available.

How it works
Vgas≈Vw×PworkV_{\text{gas}} \approx V_{\text{w}} \times P_{\text{work}}

Where

VgasV_{\text{gas}}
rated free-gas capacity (L)
VwV_{\text{w}}
internal water volume (L)
PworkP_{\text{work}}
working pressure (bar, gauge); 1 psi = 0.06895 bar

Worked example: 12 L × 232 bar ≈ 2,784 L of free gas, about 98 cu ft. Stamped ratings are rounded and real gas at high pressure holds somewhat less.

Result

2400 L / 85 cu ft conventional estimate

Frequently Asked Questions

What is the difference between water volume and rated capacity?
Water volume is the internal size of the cylinder, the number on a metric label such as 12 L. Rated capacity is the free gas it holds at its working pressure, the number on an imperial label such as 80 cu ft.
How is rated capacity calculated?
Rated capacity ≈ water volume × working pressure in bar. The conventional ideal-gas estimate for a 12 L cylinder at 200 gauge bar is 2,400 L of free gas at 1 bar at the same temperature, about 85 cu ft. This is not actual gas inventory.
Why does my cylinder's stamped rating differ?
Manufacturer ratings may use different reference pressures, temperatures, and real-gas corrections. At high pressure the difference from the conventional ideal-gas product can be substantial. Use the specification for your exact cylinder; a marketed cylinder name alone does not establish its water volume.
Does it include a reserve?
No. It converts capacity labels using a conventional approximation and does not model a reserve. Use the gas planner for conventional usable-gas planning.

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