Roofing bundles Calculator: measuring notes and method
Transfer the sloping area once
Use the actual roof surface area. If that area already includes a cutting allowance from the roof-area calculator, set waste to zero here to avoid adding it again.
CHECK A PRACTICAL EXAMPLE
A small allowance can add a whole bundle
Use 60 m² of actual roof surface and an illustrative 3 m² coverage per bundle.
No extra allowance
- Bundles to buy
- 20
- Area with waste
- 60 m²
10% extra allowance
- Bundles to buy
- 22
- Area with waste
- 66 m²
These options make the allowance visible. If the incoming area already contains an allowance, do not add that same allowance again. Ridge, hip and starter materials remain separate.
Fixed comparison in metric units. Values are illustrative unless linked to a recorded project; changing the calculator above does not change this example.
Formula
Packs = net area × (1 + waste ÷ 100) ÷ installed coverage per pack, 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
- Total surface area
- 24 m²
- Installed coverage per bundle
- 3.1 m²
- Waste allowance
- 15 %
Bundles to buy: 9
Imperial worked example
- Total surface area
- 258.3339 ft²
- Installed coverage per bundle
- 33.3681 ft²
- Waste allowance
- 15 %
Bundles to buy: 9
Follow the calculation
- Area including allowance = 24 × 1.15 = 27.6 m².
- Divide by 3.1 m² installed coverage per pack or roll, then round up to a whole purchase unit.
Reviewed 19 October 2026. How calculations are checked · Report a correction