Roof Area Calculator
Enter the building size, overhangs and pitch to get the roof area and the number of sheets.
A formula that works for any pitch
When every slope has the same angle: roof area = plan area including overhangs ÷ cos(pitch). A gable and a hip roof of the same pitch have the same total area; only the cutting differs.
Worked example
An 8 × 10 m house with 0.5 m overhangs and a 30° pitch. Plan area with overhangs: 9 × 11 = 99 m². Roof area: 99 ÷ cos 30° = 99 ÷ 0.866 = 114.3 m².
Pitch and material
| Material | Minimum pitch |
|---|---|
| Metal tile, profiled sheet | from 12–14° |
| Bitumen shingles | from 12° |
| Clay tiles | from 22° |
| Torch-on membrane | from 2–5° |
The exact limits are in the manufacturer's installation guide: below them you need solid decking, extra waterproofing or a different material.
Why you always need more sheets than area ÷ sheet area
- Sheets overlap sideways (one wave on metal tiles) and 100–150 mm lengthwise.
- A hip roof wastes up to 15–20% on angled cuts.
- Long sheets are convenient, but one cutting error ruins a whole sheet.
Besides the covering you will need ridge, eaves and verge trims, valleys, snow guards and fixings, all counted in linear metres along the matching roof lines.
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