Roofing Calculator
Roof area from footprint and pitch, squares, shingle bundles, tiles and rafter length.
About this tool
Enter the building's length and width, the eave overhang and the roof pitch as rise per 12 of run. Add a waste percentage, and in metric mode the number of tiles per square metre. The calculator shows the sloped roof area, the area with waste, roofing squares, shingle bundles, the tile count, the rafter length and the roof angle.
How roof area is calculated
A roof is larger than the footprint it covers because it slopes. Add the overhang to each side of the footprint, then multiply by the pitch factor โ(1 + (rise รท 12)ยฒ). For a gable or hip roof where every plane has the same pitch, this gives the full sloped area. A 40 ร 30 ft house with a 1 ft overhang has a plan area of 1,344 sq ft. At a 6-in-12 pitch (26.6ยฐ) the factor is 1.118, so the roof is about 1,503 sq ft. Adding 10% waste brings it to 1,653 sq ft, or 16.5 squares of 100 sq ft. At three bundles to a square that is 50 bundles of shingles, and each rafter runs about 17.9 ft from eave to ridge. Use 10% waste for a simple gable and 15% or more for hips, valleys and dormers. Honest limits: ridge caps, starter strips, underlayment, flashing and fixings are extra. Roof work is dangerous, so leave anything beyond small repairs to a professional. The stair calculator uses the same rise-and-run maths, the area calculator handles irregular footprints and the unit converter switches units.
Frequently asked questions
What is a roofing square?
100 square feet of roof area. Shingles are usually sold three bundles to a square.
How do I convert roof pitch to a multiplier?
Pitch factor = โ(1 + (rise รท 12)ยฒ). A 6/12 pitch gives 1.118, a 12/12 pitch gives 1.414.
How much waste should I allow for roofing?
About 10% for a simple gable roof and 15โ20% for hip roofs or roofs with valleys and dormers.
Is my data saved?
No. The calculation runs in your browser and nothing is stored or sent.