Pipe Volume Calculator: How Much Water Is in a Pipe
Enter the inside diameter and length of the pipe. You get the water volume in litres, US gallons and cubic metres, plus the time to fill it at your flow rate.
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Formula
- Cross-section:
A = π × (d ÷ 2)²using the inner diameter - Volume:
V = A × L 1 m³ = 1000 litres,1 US gallon = 3.785411784 litres- Fill time:
volume ÷ flow rate
Worked example
A 50 mm pipe, 100 m long. Radius = 0.025 m, so A = π × 0.025² = 0.0019635 m². V = 0.0019635 × 100 = 0.19635 m³ = 196.35 litres = 51.87 US gallons. At 20 litres per minute it fills in 196.35 ÷ 20 = 9.82 minutes.
Assumptions
- The pipe is full and straight, with a constant inner diameter.
- Fittings, valves and air pockets are not included.
- Fill time assumes a steady flow rate.
- Gallons are US gallons.
Frequently asked questions
How do I find the volume of water in a pipe?
Use V = pi x (d / 2)^2 x L with the inside diameter, not the outside. A 50 mm pipe 100 m long holds pi x 0.025^2 x 100 = 0.1963 m3, which is 196.35 litres or 51.87 US gallons.
Should I use inner or outer diameter?
Use the inner diameter, because water only fills the bore. Wall thickness changes it a lot. A nominal 2 in pipe usually has an inside diameter different from 2 in, so check the pipe schedule or the maker's data.
How long will it take to fill the pipe?
Divide the volume by the flow rate. At 20 litres per minute the 196.35 litre pipe above fills in 9.82 minutes. This assumes a steady flow and ignores air pockets and fittings.
How many litres per metre does a pipe hold?
Divide the volume by the length. The 50 mm pipe holds 1.963 litres per metre. A 2 in (50.8 mm) bore holds about 2.03 litres per metre, or 0.535 US gallons.