Pipe Volume Calculator

Internal diameter, mm

External diameter, mm

Length, m

Material

Result

Volume, litres15.71
Volume, m³0.01571
Litres per metre0.314
Surface area, m²3.93
Pipe mass, kg7.95

For expansion vessels and for lagging

How much water a pipe holds, litres per metre, external surface area and the mass of the pipe itself.

The question comes up when sizing a heating system: system volume determines the expansion vessel and how much antifreeze to buy. It is computed from the internal diameter, and confusing that with the external one is expensive.

Surface area answers a different question — how much lagging and paint the run needs. Mass matters when installing long sections; a hundred metres of steel pipe weighs well over a hundred kilograms.

What this calculator shows

Volume in litres and cubic metres, plus litres per metre
External surface area for insulation and painting
The pipe's own mass for the material selected

What to keep in mind

Volume uses the internal diameter: polypropylene has thick walls, and the gap to the external diameter reaches a third.
Densities are the reference values: steel 7850, copper 8960, polypropylene 900, PVC 1400 kg/m³.

FAQs

Internal or external diameter?

Internal, always. A pipe marked 25 mm in polypropylene has an internal bore around 16.6 mm, and using the outside figure more than doubles the answer.

How do I get total system volume?

Add pipework, radiators and boiler. An aluminium radiator section holds about 0.45 litres, a cast iron one up to 1.5; the boiler figure is in its manual.

Why calculate surface area?

For lagging and anti-corrosion paint. It also indicates heat output from exposed runs — sometimes a pipe heats a room as effectively as a small radiator.

How many litres in a metre of one-inch pipe?

A one-inch steel pipe bores about 25.5 mm, giving roughly 0.51 litres per metre. Enter your own figure for an exact answer.

Worked example

A heating circuit

Input: 20 mm internal, 25 mm external, 50 m, polypropylene

Output: 15.71 litres, 0.314 l per metre

Note: Fifteen litres in the pipework, plus radiators and boiler, gives system volume. The expansion vessel is roughly a tenth of that.

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Pipe Volume Calculator

Result

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