Enter your home's footprint (the area from a bird's-eye view) and roof pitch to find the actual sloped roof area in "squares" - the standard roofing unit, where 1 square covers 100 sq ft.
Roofing Calculator
LiveThe formula
Roof pitch is expressed as rise over a 12-inch run - a "6/12" roof rises 6 inches for every 12 inches horizontal.
A 1,500 sq ft footprint with a 6/12 pitch and 10% waste: multiplier = sqrt(36+144)/12 ≈ 1.118, roof area = 1,500 x 1.118 x 1.10 ≈ 1,845 sq ft, or 18.45 squares - about 56 bundles of standard 3-bundle-per-square shingles.
Step-by-step guide
- Find your building's footprint - the ground-level area it covers, not the roof area itself.
- Determine your roof's pitch - check your home's blueprints, or measure a 12-inch level section and see how much it rises.
- Set a waste allowance - 10% for a simple gable roof, 15-20% for one with many hips, valleys, or dormers.
- Read the squares needed and bundle count to plan your material order.
Why pitch matters so much
A flat roof's actual surface area equals its footprint. But as pitch increases, the roof surface stretches over more actual area than the footprint below it suggests - a steep 12/12 roof has about 41% more surface area than its footprint, meaning significantly more material (and often more labor cost) than a low-slope roof covering the identical footprint.
Common mistakes
Frequently asked questions
What does a "roofing square" mean?
One roofing square equals 100 square feet of actual roof surface - it's the standard unit roofing materials and labor are typically priced by.
How do I measure my roof pitch without climbing up?
From inside an attic, hold a level horizontally against a rafter and measure the vertical distance from the level to the rafter at the 12-inch mark - that's your rise. Many home blueprints also list the pitch directly.
How many shingles come in a bundle?
Most standard asphalt shingles are packaged 3 bundles per square, though this can vary by product - check your specific shingle's packaging for the exact coverage per bundle.
Should I include the underlayment and starter strips separately?
Yes - underlayment, starter strips, ridge cap, and flashing are typically ordered separately based on the same square footage and roof edge/ridge length, which this calculator doesn't itemize.
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