Roofing Calculator
Estimate roof area, roofing squares and shingle bundles from the roof footprint and its pitch.
How it works
roof area = footprint × pitch multiplier · squares = ceil(area ÷ 100) · bundles = squares × 3 (+10% waste)
A pitched roof has more surface than the ground it covers, so the flat footprint is multiplied by a slope factor — 1.118 for a 6/12 roof, up to 1.414 for a steep 12/12. Roofers count in squares of 100 sq ft, and three-tab or architectural shingles run three bundles to the square. Add about 10% for cuts, plus extra bundles for the starter strip and ridge cap.
Worked example
A 40 × 30 ft footprint is 1,200 sq ft. At 6/12 pitch (×1.118) the actual roof is about 1,342 sq ft, or 14 squares — 42 bundles, roughly 46 with waste.
Frequently asked questions
What is a roofing square?
One hundred square feet of roof surface. Shingles, underlayment and labor are all priced by the square, so converting your area to squares is the first step in any roofing estimate.
How do I find my roof pitch?
Measure the vertical rise over 12 inches of horizontal run — a 6-inch rise is a 6/12 pitch. The roof-pitch calculator turns that rise and run into the exact slope multiplier used here.
How many bundles cover a square?
Three bundles per square for standard three-tab and most architectural shingles; heavier designer shingles can run four or five. Always confirm the bundles-per-square on the specific product wrapper.
Related calculators
Estimates only — add for waste and confirm against local building codes and supplier specs.