Flashing lengths Calculator: measuring notes and method
Measure along the flashing runs
Include actual returns and specified lap lengths once. Keep different profiles as separate items even when their run lengths can be added.
Check width and fabrication
Compare individual cut lengths with available stock. Corner pieces and folds need a fabrication schedule alongside the total run length.
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
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