Roof area from footprint and pitch.
Convert your roof footprint and pitch into true surface area in square feet, square metres, and roofing squares.
Roof Area Calculator
This is one of six interlinked roofing calculators. For a complete material list across a multi-plane roof, use the full roofing material calculator.
The roof area calculator converts a plane's footprint and pitch into true surface area in square feet, square metres, and roofing squares — the starting point for any material estimate.
How to use this calculator
- Footprint length & width (ft)
- The flat, ground-level dimensions of the roof plane, as if viewed straight down. Measure from plans, the ground, or a satellite tool.
- Pitch (rise:12)
- The slope, in inches of rise per 12-inch run. The calculator uses this to scale the footprint up to true surface area.
How we calculate it
True area = footprint × pitch multiplier. The footprint is length × width. The pitch multiplier is √(12² + rise²) ÷ 12 — for a 6:12 roof that's 1.118, so the real surface is 11.8% larger than the ground shadow.
Squares are the true area divided by 100. Square metres are the true area × 0.0929. We report all three because suppliers quote in squares, plans are often in square feet, and metric users need m².
A flat (0:12) roof has a multiplier of 1, so its true area equals its footprint. The steeper the roof, the larger the correction.
A worked example
A roof plane with a 40 ft × 30 ft footprint at a 6:12 pitch.
- Footprint = 40 × 30 = 1,200 sq ft.
- 6:12 multiplier = √(144 + 36) ÷ 12 = √180 ÷ 12 = 1.118.
- True area = 1,200 × 1.118 = 1,342 sq ft.
- Squares = 1,342 ÷ 100 = 13.4 (before waste). Square metres = 1,342 × 0.0929 = 124.7 m².
A 1,200 sq ft footprint at 6:12 is about 1,342 sq ft of actual roof — 13.4 squares before any waste allowance.
Frequently asked questions
Do I add waste here?
This calculator reports true area; the full calculator and bundle calculator add the waste allowance when converting to a material order.
What if my roof has several planes?
Calculate each plane separately and add the areas, or use the full calculator's multi-section builder to do it in one place.
Why not just measure the roof directly?
Footprint measurements are far safer and easier to take from the ground or plans than climbing a pitched roof with a tape.