About this calculator
How much water a pipe run holds, useful for purging, antifreeze, system fill and working out how long a tap takes to run hot.
How it’s calculated
Volume = π × (inside diameter)² ÷ 4 × length. Purge time = volume ÷ tap flow rate.
Worked example
With these inputs:
- Pipe
- Copper 15 mm
- Length of run
- 15 m
- Tap flow rate (L/min)
- 6
the result is:
- Water in the pipe
- 2.2 L
- Inside diameter
- 13.6 mm
- Per 10 m
- 1.5 L
- Time to purge (wait for hot water)
- 22 seconds
- Water weight
- 2.2 kg
Tips from the trade
- Long hot-water runs in large pipe waste water and time. Consider a smaller dedicated run or a recirculation loop.
Results are estimates for planning and pricing. Check quantities against your drawings, the manufacturer’s data and the Building Regulations before ordering.