Roofing CalculatorFree online other calculator — instant results, no sign-up

Roof Area = Footprint Area × √(1 + (Pitch / 12)²)
Squares = Roof Area / 100
Bundles = ceil(Squares × 3 × 1.10)

• Roof AreaTrue surface area of the pitched roof in square feet
• Footprint AreaHorizontal plane area under the roof in square feet
• PitchVertical rise in inches per 12 inches of horizontal run
• SquaresRoofing unit equivalent to 100 square feet of roof surface
• BundlesTotal bundles of shingles needed, assuming standard 3 bundles per square plus a 10% allowance for waste

The tool calculates true surface area by multiplying the horizontal footprint by a pitch multiplier derived from the Pythagorean theorem, √(1 + (Pitch / 12)²). Roofing squares are determined by dividing the calculated roof area by 100 and rounding to one decimal place. Total bundle count assumes standard 3-tab or architectural shingles (3 bundles per square) with an added 10% waste factor, rounded up to the nearest whole bundle.

These are the calculator's starting values and the results it actually produces for them.

1. 1Divide the pitch value by 12, square the result, add 1, and take the square root to find the roof pitch multiplier.
2. 2Multiply the horizontal footprint area by the pitch multiplier to determine total sloped roof area in square feet.
3. 3Divide the total roof area by 100 to calculate the number of roofing squares.
4. 4Multiply roofing squares by 3 bundles per square and 1.10 for waste, then round up to the next whole integer to get total bundles.

Further reading

• Wolfram MathWorld - Pythagorean Theorem