Roof Area Calculator
A pitched roof covers more surface than the ground beneath it. Enter your building's footprint and the roof pitch for the true sloped area — in square feet and in roofing squares.
Roof area
1,677sq ft
- Roofing squares
- 16.8 squares
How it’s calculated
Roof area = footprint × √(12² + rise²) ÷ 12, where rise is the pitch in 12. The square-root term is the slope factor — how much longer the sloped surface is than its horizontal run. Roofing squares = roof area ÷ 100.
Worked example
A 1,500 sq ft footprint at 6/12 pitch: slope factor = √(144 + 36) ÷ 12 ≈ 1.118, so roof area ≈ 1,677 sq ft = 16.8 squares.
FAQs
- Why isn't my roof area the same as my floor area?
- Because the roof is sloped. A 6/12 roof has about 12% more surface than the footprint it covers; a 12/12 (45°) roof has about 41% more. The steeper the pitch, the bigger the gap — which is exactly what the multiplier captures.
- What's a roofing square?
- 100 square feet of roof surface — the unit roofing materials are priced and ordered by. A 2,000-square-foot roof is 20 squares.
- Does this handle hips, valleys, and dormers?
- It's the area for a simple gable footprint. Complex roofs with lots of hips, valleys, and dormers have more surface and more cutting waste — measure each plane separately and add them for a complex roof.
Sources
- Roof area = footprint × √(12² + rise²) ÷ 12 (slope factor, geometry). Roofing square = 100 sq ft (convention).