Cylinder & Tube Capacity Calculator
Find out how much gas a cylinder, tube, tube trailer or storage vessel holds — in standard cubic feet (SCF), for every common gas at once.
- 1Enter the vessel's water volume, in cubic feet or gallons.
- 2Enter the fill pressure in PSIG.
- 3Press Calculate. You'll see how many SCF it holds for each gas.
How it works
Real gases don't compress evenly — each gas packs differently as pressure rises, so the simple “pressure ÷ 14.7” rule can be off by 10% or more. This calculator accounts for that using each gas's compressibility.
Z is the gas's compressibility factor at the fill pressure, taken from NIST reference data for each gas. Standard conditions are 70°F and 14.696 psia, the US industrial gas convention. Results assume the gas is at 70°F; a hot or cold fill will read differently on the gauge.
Natural gas values are for typical pipeline gas, which contains heavier hydrocarbons than pure methane and holds a few percent more. Your gas supplier's composition may differ.
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Frequently Asked Questions
Common questions
What is SCF?
Standard cubic feet — the volume a gas would take up at standard conditions (70°F and atmospheric pressure, 14.696 psia, the US industrial gas convention), regardless of what pressure it's actually stored at. It's how gas quantity is measured and sold, since the same SCF of gas takes up very different physical space depending on pressure.
What's the difference between PSIG and PSIA?
PSIG (gauge pressure) is what a pressure gauge reads — pressure above the surrounding atmosphere. PSIA (absolute pressure) includes the atmosphere itself, so it's PSIG plus about 14.7. Cylinder fill pressures are almost always given in PSIG, which is why this calculator asks for PSIG and adds atmospheric pressure internally.
Why does the same cylinder hold a different amount of different gases at the same pressure?
Every gas compresses a little differently as pressure rises — a property called compressibility. Light gases like helium and hydrogen behave close to the simple textbook "ideal gas" prediction, while others depart more, especially at higher pressures. That's why this calculator runs the math separately for each gas instead of using one number for all of them.
Does gas capacity scale exactly with pressure — like double the PSIG, double the gas?
No, not exactly, and that gap grows with pressure. A simple "pressure ÷ 14.7" estimate can be off by several percent or more at high pressure, because it assumes gas compresses in a perfectly straight line, which real gases don't. This calculator accounts for that directly rather than using the simplified shortcut.
What's "water volume," and why isn't it just the cylinder's size?
Water volume is the internal volume of the vessel — how much water it would take to fill it completely. It's the number stamped on a cylinder's nameplate and the standard way vessel size is specified in the industry, so it's what this calculator (and manufacturers) use as the input, rather than external dimensions.
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