Roofing calculator

Convert horizontal roof projection area to sloping area using √(rise² + run²)/run.

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Total horizontal roof projection area

Rise per run

More inputs and assumptions

Run used for pitch

Waste allowance (%)

Answer

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Convert horizontal roof projection area to sloping area using √(rise² + run²)/run.

More results

Precision and calculation record

Decimal places in numeric results and text downloads

Rounding changes displayed numbers, not the calculation. Text, fractions, matrices and CSV schedules keep their own formatting. Automatic keeps up to 12 significant digits, with money shown to cents where applicable.

Saved scenario

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Formula and assumptions

Every roof plane must share the entered pitch. Include overhangs in the horizontal projection and avoid counting overlap twice. Waste is your estimate. Valleys, product exposure, fastening and structural requirements are not designed.

Automatic precision shows numbers to 12 significant digits. Thousands separators such as 1,000 are accepted; use a dot for decimals.

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Updated 2026-09-26

Using Roofing calculator

Convert horizontal roof projection area to sloping area using √(rise² + run²)/run.

Next: Roof pitch calculator

A worked example

Example inputs: total horizontal roof projection area = 100, rise per run = 6, run used for pitch = 12, waste allowance (%) = 10. Sloping roof area = 111.803398875.

Before you use the result

Example results for total horizontal roof projection area

These examples use Rise per run: 6; Run used for pitch: 12; Waste allowance (%): 10. They are reference calculations, not recommended settings.

Total horizontal roof projection area	Sloping roof area
50	55.9016994375
100	111.803398875
200	223.60679775

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ToolOctopus. “Roofing calculator.” Updated 2026-09-26. https://tooloctopus.com/roofing-calculator.

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