Roofing Calculator
A roofing calculator estimates the material needed to cover a roof, accounting for the pitch (slope) which increases actual roof area beyond the building footprint. Roofing material is measured in "squares" — one square covers 100 square feet.
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Tip: Three bundles of standard 3-tab shingles cover one roofing square (100 sq ft). Architectural/dimensional shingles vary — check the bundle coverage on the package.
- 1Measure the building footprint: length × width
- 2Calculate pitch factor: √(1 + (rise/run)²) where run is typically 12"
- 3Actual roof area = footprint × pitch factor × (number of roof sections)
- 4Add 10–15% waste for ridge caps, valleys, and cuts
- 5Divide by 100 to get squares; multiply by 3 for shingle bundles
40×30 ft house, 6/12 pitch, 15% waste=~15 squares, 45 bundlesPitch factor: √(1+0.25) = 1.118
| Pitch (x/12) | Angle | Pitch Factor | Description |
|---|---|---|---|
| 2/12 | 9.5° | 1.014 | Low slope (nearly flat) |
| 4/12 | 18.4° | 1.054 | Common ranch homes |
| 6/12 | 26.6° | 1.118 | Very common, good drainage |
| 8/12 | 33.7° | 1.202 | Steep — good attic space |
| 12/12 | 45° | 1.414 | Very steep |
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Fun Fact
Asphalt shingles — the most common roofing material in North America — last 20–30 years. Metal roofing lasts 40–70 years and reflects more heat, reducing cooling costs.
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