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Roofing Calculator
Enter your house footprint and roof pitch. The calculator estimates the actual slope area, converts to squares, and rounds up to whole bundles of shingles with a waste allowance and optional cost estimate.
House and roof
Enter the house footprint and the roof pitch (rise over a 12-inch run). The calculator multiplies the footprint by the pitch factor to estimate the slope area.
Roof pitch (rise per 12 in run)
0 for flat; 12 means 45 degree pitch.
10 to 15 percent is typical.
Architectural shingles cover about 33.3 sq ft/bundle (3 bundles per square).
Leave blank to skip the cost estimate.
Assumptions
- Simple gable roof (two-slope) over a rectangular footprint.
- Pitch multiplier = sqrt(1 + (rise / 12)^2).
- 1 roofing square = 100 sq ft. Standard 3-tab and architectural shingles ship as bundles that together cover one square.
- Complex rooflines (hips, valleys, dormers, multiple pitches) need professional measurement.
- Educational estimate. Not a contractor quote, structural opinion, or code-compliance check.
Bundles needed
45 bundles
Roof area 1,341.64 sq ft = 13.42 squares
Order whole bundles. The bundle count above is rounded up to the next whole bundle to cover the waste allowance.
Examples
40 x 30 ft house, 6/12 pitch, 10% waste
≈ 1,342 sq ft, 13.4 squares, 45 bundles
30 x 25 ft, 4/12 pitch, 10% waste
≈ 791 sq ft, 7.9 squares, 27 bundles
50 x 40 ft, 8/12 pitch, 15% waste
≈ 2,404 sq ft, 24 squares, 84 bundles
Flat 30 x 30 ft, 5% waste
≈ 900 sq ft, 9 squares, 29 bundles
How it works
Roof area is the house footprint multiplied by a pitch factor. The factor accounts for the extra surface that a slope creates compared to a flat plan.
Pitch multiplier · m = sqrt(1 + (rise / 12)^2)
Roof area · A = (length x width) x m
1 square = 100 sq ft. Most shingles cover 1 square with 3 bundles.
Related home calculators
- Square footage calculator for general area math when you only need flat square footage.
- Area calculator for non-rectangular shapes that you may need to add up separately.
- Pythagorean theorem calculator for the slope length when you know rise and run.
- Triangle area calculator for gable-end siding and similar triangular areas.
- All home calculators.
Frequently asked questions
The footprint is the flat area you see from above. A pitched roof slopes, so its actual surface is larger. The calculator multiplies the footprint by a pitch factor (the square root of 1 plus (rise/12) squared) to get the slope area.
A square is 100 square feet of roof surface. Roofers and material suppliers quote in squares because most shingle products are sold in bundles that cover one square (typically three bundles).
Pitch is the rise of the roof in inches over a 12-inch run. Low-slope roofs are 3/12 or less. Standard residential is around 6/12. Steep roofs are 8/12 or higher. If you do not know the pitch, measure with a level and a tape, or ask the contractor.
Allow 10 percent for a simple gable roof. Add another 5 percent (15 total) for hips, valleys, and other complex cuts. Architectural shingles waste a bit more than 3-tab because of the staggered pattern.
This calculator assumes a simple gable (two slopes over a rectangle). For hip, mansard, or multi-pitch roofs, measure each plane separately and add the surface areas. Or take the calculator's number as a rough first pass and order from a measured estimate.
No. The calculator returns an educational estimate to help you understand quantity and order of magnitude. It does not factor in tear-off, underlayment, flashing, ridge cap, drip edge, ventilation, labor, or local code. Always get a written quote from a licensed roofer for actual work.
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