Downpipe lengths Calculator: measuring notes and method
Follow the pipe route
Measure vertical drops and any offset pipe sections along their actual route. Use separate entries where drops differ rather than multiplying one typical length by every downpipe.
Prepare a fittings list
Count bends, shoes, sockets and clips individually. Their connection details can change the length of straight pipe required between them.
Formula
Required length = length per run × runs × (1 + waste ÷ 100). Stock count = required length ÷ stock length, rounded up.
Worked examples in metric and imperial units
Illustrative values match Reset example and stay fixed when you edit the calculator. Both columns describe the same calculation; converted inputs are rounded.
Metric worked example
- Required length per run
- 6 m
- Quantity
- 1
- Stock length
- 3 m
- Waste allowance
- 10 %
Stock lengths to buy: 3
Imperial worked example
- Required length per run
- 19.685 ft
- Quantity
- 1
- Stock length
- 9.8425 ft
- Waste allowance
- 10 %
Stock lengths to buy: 3
Follow the calculation
Lengths in this working are in metres.
- Net required length = 6 × 1 = 6 m.
- Stock count = 6 × 1.1 ÷ 3, rounded up. This assumes usable offcuts.
Reviewed 19 October 2026. How calculations are checked · Report a correction