How to calculate roofing
Roof area = Footprint × √(1 + (rise ÷ 12)²) Squares = Roof area × (1 + waste) ÷ 100
Worked example. Roofing squares needed: 24.6.
Example inputs — Home footprint incl. overhangs: 2,000 sq ft; Roof pitch: 6/12; Waste allowance: 10%. Starting values are illustrative.
From George Guju, founder of Calculyn · Educational calculator guidance, not professional advice.
How it works
A sloped roof has more surface than the floor beneath it. Multiplying the footprint by the pitch multiplier gives the true roof area. Roofers sell in squares (100 sq ft), and most shingles come 3 bundles per square.
Assumptions & limitations
- Simple gable or hip roof with one pitch.
- Excludes ridge caps, starter strips and underlayment.
Formula and assumptions reviewed October 2026 by the Calculyn team. How we build our calculators
Frequently asked questions
How do I find my roof pitch?
Measure how many inches the roof rises over 12 inches of horizontal run. A 6-inch rise is a 6/12 pitch.