Roofing Calculator
Estimate the total roof area, roofing squares, and shingle bundles needed for your roof based on its footprint and pitch.
What this calculator does
The roofing calculator estimates the actual sloped surface area of your roof and converts it into roofing squares and shingle bundles, the units roofing material is bought in.
The formula
A sloped roof covers more surface area than the building’s flat footprint. Multiplying the footprint by a pitch multiplier of sqrt(1 + (pitch/12)²) accounts for the slope. A waste allowance (typically 10%, more for cut-up roofs with many hips, valleys, and dormers) is added, and the total is divided by 100 to get roofing “squares” — the standard 100-square-foot unit. Standard three-tab and architectural asphalt shingles are commonly packaged 3 bundles per square, so squares are multiplied by 3 and rounded up for bundle count.
This is a material planning estimate. Always add extra for starter strips, ridge caps, and complex roof features, and confirm bundle coverage with your specific shingle product.