Roofing Calculator
Last updated: June 2026 · Free · No sign-up required
Enter values above and click Calculate to see your result instantly.
Quick reference
| Pitch (rise/12) | Multiplier |
|---|---|
| 4/12 | 1.054 |
| 6/12 | 1.118 |
| 8/12 | 1.202 |
| 12/12 | 1.414 |
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Responsive design tested down to a 320px-wide phone screen. The input fields use native number/date keyboards on iOS and Android, the calculate button is thumb-sized, and the result still reads big and bold on the smallest screen. No app to download, ever.
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Interpretation guide
| Unit | Equivalent |
|---|---|
| 1 roofing square | 100 sq ft |
| Shingle bundles | 3 per square |
| Waste allowance | add 10–15% |
Formula & methodology
Formula: Roof area = footprint area × √(1 + (rise/12)²); squares = area / 100
A sloped roof covers more area than its flat footprint. The pitch multiplier scales the footprint up to the true roof surface.
- Footprint area = length × width.
- Pitch multiplier = √(1 + (rise/12)²).
- Roof area = footprint area × multiplier.
- Squares = roof area ÷ 100; bundles = squares × 3 (plus 10% waste).
Worked example: A 40 × 30 ft footprint at 6/12 pitch is 1,200 × 1.118 = 1,342 ft³ = 13.4 squares.
Frequently asked questions
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