Roof area calculator
Turn a building footprint or a list of roof planes into sloped roof area and roofing squares. Overhangs, pitch and hip or gable shape are included, with eave, rake, ridge and hip lengths for ordering trim.
Building length and width up to 1,000 m (3,280.8 ft), overhangs from 0 to 5 m (16.4 ft), pitch from 0 to 48 per 12, 0 to 75 degrees or 0 to 400%, and up to 200 plane rows with counts from 1 to 100 in up to 100,000 characters. Calculated on your device; download a JSON report, a results CSV and a roof planes CSV. This calculator uses the measurement fields only. Up to 1,000,000 characters. Review the settings before running.
Your result
How to use Roof area calculator
- Choose a building footprint for a simple gable, hip or shed roof, or a list of roof planes for anything more complex.
- Enter the outside wall dimensions and level overhangs, or one plane per line with its plan length, width and pitch.
- Pick how the pitch is entered: rise per 12, an angle or a percent slope.
- Review the sloped area, squares and edge lengths, then download the JSON report or the CSV files.
Useful next steps
From plan area to sloped area
A flat roof plane covers more surface than its footprint. Its sloped area is the level plan area times √(1 + (rise ÷ run)²), which equals 1 ÷ cos(roof angle) (OpenStax Precalculus 2e, 5.4 Right Triangle Trigonometry, checked 16 October 2026). A 6/12 roof has a factor of 1.118034, so a 42 × 32 ft footprint with overhangs (1,344 ft²) has 1,502.64 ft² of roof.
Footprints and overhangs
Overhangs are measured level, from the wall to the fascia or rake edge. A gable or shed roof adds the rake overhang at both ends and the eave overhang on both long sides. A hip roof adds the eave overhang all round and puts the ridge along the longer side, so a 13 × 9 m hip footprint has a 4 m ridge and four hips. When every plane shares one pitch, the whole roof is the plan area times one factor.
Complex roofs, plane by plane
Fine Homebuilding recommends breaking a complex roof into rectangles and triangles (Mike Guertin, How to Estimate Materials for Roofing Projects, checked 16 October 2026). Enter each plane with its level length and width; triangles count half, and a trapezoid can be entered as a rectangle using the average of its two parallel sides. Each plane may have its own pitch.
Squares and limits
A roofing square is 100 ft² of roof surface (Wikipedia, Square (unit), checked 16 October 2026). Waste, starter and ridge cap are added in the roof shingle calculator. The estimate assumes flat planes and does not check structure, drainage or roofing code minimum slopes. Unit conversions use NIST SP 811 factors.