Roofing Calculator
Convert footprint and pitch into shingles.
Your numbers
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Your results
Footprint with overhang (sq ft)
Footprint with overhang (sq ft)
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Roof area (sq ft)
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Roofing squares to buy
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Shingle bundles (3 per square)
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Roofing Calculator by TheCalcTools
How the Roofing Calculator works
Enter the building footprint and the eave overhang.
A pitch factor converts flat area into sloped surface area.
One roofing square covers 100 sq ft and three bundles cover a square.
The formula
Roof area = footprint × √(1 + (pitch ÷ 12)²)1 square = 100 sq ft
Worked example
Using the default values shown in the calculator:
| Building length (ft) | 40 |
|---|---|
| Building width (ft) | 28 |
| Eave overhang each side (ft) | 1 |
| Pitch (rise per 12 in run) | 6 |
| Waste allowance | 10 % |
- Footprint with overhang = 42 × 30 = 1,260 sq ft.
- Pitch factor √(1 + 0.5²) → roof area 1,409 sq ft; buy 15.5 squares (47 bundles).
Result:
| Footprint with overhang (sq ft) | 1,260 |
|---|---|
| Roof area (sq ft) | 1,409 |
| Roofing squares to buy | 15.5 |
| Shingle bundles (3 per square) | 47 |
Frequently asked questions
What does a 6/12 pitch mean?
The roof rises 6 inches for every 12 inches of horizontal run, about 26.6 degrees.
Does this work for complex roofs?
It suits simple gable and hip roofs. Add areas for dormers and valleys, and ask a roofer to confirm.
Sources and further reading
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This calculator gives estimates for information only. Check important results independently before you rely on them. See our disclaimer.