Roofing calculator
Roof area from the house footprint and pitch, in squares and bundles of shingles.
About this calculator
This roofing calculator estimates the area of a roof from the size of the house, the overhangs and the roof pitch.
It converts the area into roofing squares and bundles of shingles, with extra for waste, and can price the shingles too.
How it works
With one pitch on every face, the roof area is the footprint, including the overhangs, × the pitch multiplier √(12² + rise²) ÷ 12. A roofing square is 100 square feet (about 9.3 m²), usually 3 bundles of asphalt shingles.
Last reviewed:
Worked example
- Measure in: Feet
- House length: 40
- House width: 30
- Eave overhang on each side: 1
- Roof pitch: 6/12 (27°)
- Extra for waste and cuts: 10%
- Bundles per square: 3
Roof area: 1,503 ft² (139.6 m²)
Common questions
What is a roofing square?
100 square feet of roof, about 9.3 m². A roof of 2,000 square feet is 20 squares.
How many bundles of shingles are in a square?
Usually 3 for standard asphalt shingles. Some heavier designer shingles need 4 or 5, so check the packaging.
What does a 6/12 roof pitch mean?
The roof rises 6 inches for every 12 inches across, an angle of about 26.6°. Its area is about 1.118 times its footprint.
Sources and further reading
The story behind it
Where the idea came from: Asphalt shingles were first made in the United States in the early 1900s, and they now cover most American homes.
Roofers measure in squares of 100 square feet. A sloping roof has more surface than the ground it covers, so the pitch multiplier turns the plan view into the real area to cover.
Why you can trust this calculator
- It runs in your browser. Nothing you type into it is sent anywhere.
- The method is explained on this page, so you can check it yourself.
- Free to use, with no sign-up.
- Results are estimates, so please double-check anything important.
- Spotted a mistake? Tell us and we'll look into it.
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