Pipe Volume Calculator
Calculate how many litres of water a pipe holds and how long it takes to flush or fill it.
Inputs
Formula
- Volume = π/4 × D² × L
- Litres = volume in m³ × 1000
- Fill time = volume ÷ flow
The volume inside a pipe is the cross-sectional area times the length. It matters when you are flushing a new line, dosing chlorine, or estimating how much water is wasted waiting for hot water to arrive at the tap.
Step-by-step calculation
- 1
Area
π/4 × D²
804.2 mm²
- 2
Volume
area × length
0.02011 m³
- 3
Litres
× 1000
20.11 L
Worked example
- 1A 32 mm pipe, 25 m long: area = π/4 × 0.032² = 0.000804 m².
- 2Volume = 0.000804 × 25 = 0.0201 m³ = 20.1 litres.
- 3At 60 lpm it flushes in 20 seconds.
Tips
- Use the inside diameter, not the outside — PVC pipes are named by outside diameter.
- Flush at least three pipe volumes when disinfecting a new line.
Frequently asked questions
How many litres in a 1 inch pipe per metre?
About 0.5 litres per metre for a 25 mm bore.
Is nominal size the inside diameter?
Not always. PVC is named by outside diameter, GI by nominal bore — check the wall thickness.
Why does this matter for hot water?
The pipe volume is exactly the cold water you waste before hot water reaches the tap.
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