HesapHanem

Pipe Volume Calculator

Enter the inner diameter and length to find the pipe's internal volume.

How it is calculated

The pipe is treated as a straight cylinder: V = π × r² × L. The inner diameter is entered in centimetres and the length in metres; the tool converts the diameter to metres and halves it for the radius r = (d / 100) / 2. Volume in cubic metres is then multiplied by 1000 for litres, and litres are divided by 3.785 for US gallons. Both inputs must be above zero. Litres and gallons are rounded to two decimals and cubic metres to four. The volume covers a full, straight pipe, without fittings, bends or partly filled sections, and it is not an imperial gallon figure.

Worked example

A pipe with an inner diameter of 5 cm and a length of 20 m. Radius: 5 / 100 / 2 = 0.025 m. Volume: π × 0.025² × 20 = 0.03927 m³, shown as 0.0393 m³. In litres: 0.03927 × 1000 = 39.27 L. In US gallons: 39.27 / 3.785 = 10.38 gal. So flushing this run of pipe takes about 39 litres.

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Common mistakes

  • Entering the outer diameter or the nominal pipe size. Wall thickness takes away from the bore, so the real inner diameter is smaller and the volume smaller too.
  • Entering the diameter in millimetres or inches. The field is in centimetres, so 50 for a 50 mm pipe would overstate the volume tenfold in diameter and a hundredfold in volume.
  • Entering the length in centimetres or feet. The length must be in metres.
  • Entering the radius instead of the diameter. Because the radius is squared, entering 2.5 for a 5 cm diameter gives a quarter of the correct volume.
  • Using the gallon figure for UK (imperial) gallons. It is divided by 3.785, the US gallon.

About this calculator

The liquid a pipe can hold is a straight cylinder volume problem: V = π × r² × L, where r is the pipe’s inner radius (half the inner diameter, not the outer or nominal pipe size) and L is its length. Because pipe walls have thickness, the inner diameter is always a bit smaller than the labeled nominal size, so using the true bore is what makes the result accurate.

Plumbers, irrigation designers and process engineers use this figure to size holding volumes, estimate purge or flush volumes before a chemical changeover, calculate fluid weight for structural supports, or work out how much water is trapped in a run of pipe during draining or dosing. This calculator converts the resulting volume into liters, US gallons and cubic meters so it is usable across trades and regions.

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Comments (1)

  • Editorial team

    Enter the inner diameter, not the outside one, since pipe is usually sold by a nominal size and the wall takes up part of it. A 5 cm bore running 10 m holds 19.63 L, which is a handy figure when you are working out how much liquid fills a line before it reaches the far end. Fittings and bends are not counted. What is the pipe in your case used for?

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