Roofing Area Calculator
Estimate sloped roof surface area from a rectangular horizontal projection and an entered roof pitch.
How to use this calculator
- Measure the relevant dimensions and select each input’s unit. Changing units converts your entered value.
- Use the coverage, dimensions or yield for the actual product you plan to buy. The starting numbers are worked examples.
- Calculate, review the assumptions below and check the final order against the project and supplier information.
Formula
Sloped area = horizontal projected area ÷ cos(pitch in degrees). Order area = sloped area × (1 + allowance/100).
Worked example
A 10 m × 8 m total horizontal projection at 30° has 92.376 m² of sloped area; 10% allowance gives 101.614 m².
Common mistakes and limitations
Uniform-pitch planar area only. Include overhangs in the horizontal dimensions. No dormers, valleys, mixed pitches, roof loads, fastening, overlap or cutting plan. Covering product requirements must be checked separately.
Questions about roofing area
Do these dimensions include overhangs?
Enter the full horizontal projection you intend to cover, including any measured overhangs. Do not enter sloped length as horizontal length.
Can it handle roofs with different pitches?
Calculate each uniform-pitch portion separately. Do not use one angle for a roof whose surfaces have different pitches.