Roofing Calculator
Calculate the roof area and estimate materials for a gable roof.
Roof Area
How to use the Roofing Calculator
- Enter the house length and width in metres.
- Enter the roof pitch in degrees.
- Enter the overhang in cm (eaves projection).
- Click Calculate to see rafter length, roof area and roofing squares.
Formula used
This assumes a simple gable roof with two equal slopes. One roofing square = 100 sq ft.
Worked example
House 10 m × 8 m, 30° pitch, 50 cm overhang
Rafter length ≈ 5.20 m; roof length = 11 m
Roof area ≈ 114.3 m²
≈ 12.3 roofing squares
Pitch in degrees vs ratio
Roof pitch is sometimes given as a ratio such as 6/12 (6 units rise per 12 run), which is about 26.6°; 4/12 is 18.4° and 12/12 is 45°. Steeper roofs shed rain faster, which matters in heavy-monsoon regions, but need more material. Metal sheet roofs in India commonly use 10–20°, while clay tile roofs need 25–35°.
Tips for accurate results
- Add 10–15% for ridges, cuts and overlaps when buying sheets or tiles.
- Hip roofs need a more detailed calculation than a gable roof.
- Measure the overhang from the wall face to the edge of the eave.
Frequently Asked Questions
A unit equal to 100 square feet (about 9.29 m²) of roof surface.
Use arctan(6/12), which is about 26.6°.
For a flat roof, simply use length × width plus overhangs.
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Content reviewed by Vinod, Easy Smart Calculator · Last updated October 2026