Roofing Calculator

From footprint to shingles

A roof's actual surface is larger than the building's footprint because it slopes. This calculator multiplies your footprint by a pitch factor to get the true roof area, converts it to roofing "squares" (100 ft² each), adds waste, and estimates the shingle bundles you'll need.

Squares and bundles

Roofers measure in squares: 1 square = 100 ft². Standard three-tab and architectural shingles come three bundles to the square, which is the figure used here. Always round up to whole bundles and keep a spare for repairs.

FAQ

Why does pitch matter so much?

A steeper roof has more surface area over the same footprint — a 12:12 roof is about 41% larger than a flat one. The pitch factor captures that, so picking the right slope is the single biggest driver of your material count. This estimate excludes hips, valleys, and ridge caps; add extra for complex roofs.

What is a roofing "square"?

A square is 100 square feet of roof surface, the unit roofers use to order materials. Standard three-tab and architectural shingles come three bundles to the square, which is the figure this calculator uses.

How much waste should I add?

A common allowance is around 10% for simple gable roofs and 15% or more for roofs with many hips, valleys, and cuts. Add waste to cover trimming and mistakes, then round up to whole bundles and keep a spare for future repairs.

Is this an exact material order?

No, treat it as an estimate. It excludes hips, valleys, ridge caps, starter strip, and underlayment, and complex roofs need extra. Confirm quantities with your supplier or contractor before ordering.

Is the calculator free, and does it work on mobile?

Yes to both. It is free with no sign-up, runs in your browser so your measurements stay on your device, and works in any phone browser so you can estimate on the job site.