Roof Area Calculator

How this calculator works

For each roof plane, the calculator multiplies length × width to get the plane's surface area. If you enter a roof pitch (rise / 12), the calculator applies the slope multiplier √(1 + (rise/12)²) to convert plan dimensions to actual sloped dimensions.

The total roof area is the sum of all plane areas. From there:

• Squares = ceil(total area / 100) — the roofing industry's standard unit
• Square yards = total area / 9
• Square meters = total area / 10.764

Formula

slope_mult = √(1 + (pitch/12)²)  [optional, = 1 if measuring sloped dims]
plane_area_i = length_i × width_i × slope_mult
total_roof_area = Σ plane_area_i
squares = ceil(total_roof_area / 100)
sq_yd = total_roof_area / 9
sq_m = total_roof_area / 10.7639104

Example

For a gable roof with two planes of 30 ft × 20 ft each, entered as plan dimensions with a 6:12 pitch:

• slope_mult(6:12) = √(1 + 0.25) = 1.118
• plane_area = 30 × 20 × 1.118 = 670.82 sq ft each
• total = 2 × 670.82 = 1,341.64 sq ft
• = 14 squares
• = 149.07 sq yd
• = 124.66 m²

Important assumptions

• Enter up to 4 roof planes. For complex roofs with more planes, calculate sections separately and add the results.
• If your length and width are actual sloped measurements (e.g. measured with a tape on the roof), leave the pitch field blank — the multiplier defaults to 1.0.
• If your length and width are plan (footprint) measurements from a satellite image or property survey, enter the roof pitch to convert to actual sloped area.
• 1 roofing square = 100 sq ft of sloped roof area.
• This calculator does NOT add a waste factor — use the Roofing Calculator for material estimates with waste.