Pipe Volume Calculator

Calculate the internal volume of a pipe in litres and gallons from its diameter and length, for plumbing and heating systems.

Part of:Plumbing hub
mm
m

How to Use This Calculator

How to Use

  1. Enter the internal (bore) diameter of the pipe — not the outside diameter.
  2. Enter the total length of pipe.
  3. Read the volume in litres, US gallons and UK gallons.

Why internal diameter matters

The volume of water a pipe holds depends on the internal bore, which can be noticeably smaller than the quoted size once you allow for the wall thickness. For accurate results use the actual internal diameter.

Uses

Knowing pipe volume helps you size expansion vessels, work out how much water a system holds for dosing inhibitor, estimate flushing volumes and calculate how long it takes to drain or fill a run of pipe.

Common Questions

How do I calculate the volume of water in a pipe?

Use the formula volume equals pi times the radius squared times the length, with the internal radius. This calculator does it and converts to litres and gallons.

Should I use the internal or external diameter?

Always use the internal (bore) diameter. The external size includes the pipe wall, which does not hold water.

How many litres are in a metre of 15mm pipe?

About 0.18 litres per metre for 15mm internal bore. Larger pipes hold much more, for example 22mm holds around 0.38 litres per metre.

Why do I need to know pipe volume?

It is useful for sizing expansion vessels, dosing system inhibitor, estimating flushing water and working out fill and drain times.

Does pipe material change the volume?

Only through the internal bore. Copper, plastic and steel pipes of the same nominal size can have slightly different internal diameters, so check the actual bore.

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