Roofing Calculator
Squares, shingle bundles & underlayment for a roof
Re-roofing a house or shed? Enter the building footprint and roof pitch to estimate the roofing squares, bundles of shingles and rolls of underlayment you'll need, with waste already added.
How to measure a roof in squares
Roofers price work in squares — one square is 100 ft² of finished roof. The roof area is larger than the footprint of the house because the slope adds length. Measure the footprint (the ground area the roof covers), then apply a pitch multiplier to get the true sloped area. We add 10% waste for cuts, hips, valleys and starter courses.
Roof pitch and the area multiplier
Pitch is the rise in inches per 12 inches of run. A 6/12 roof rises 6 inches per foot and has an area about 1.12× its footprint; a steep 12/12 is 1.41×. Pick your pitch from the list and the calculator applies the right factor. If you can safely measure the actual roof planes instead, enter those and choose "flat" to skip the multiplier.
Shingle bundles and underlayment rolls
Asphalt shingles come 3 bundles to a square (each bundle covers about 33 ft²), so a 20-square roof needs roughly 60 bundles. Add one roll of #15 felt or synthetic underlayment per ~400 ft², plus drip edge, starter strip and ridge cap — those are sold separately from the field shingles.
Roofing Calculator: frequently asked questions
How many bundles of shingles do I need?
Three bundles per roofing square (100 ft²), so divide your roof area by about 33. A 2,000 ft² roof needs roughly 60 bundles plus waste.
What is a roofing square?
100 square feet of roof surface. Shingles, underlayment and labor are all estimated and priced by the square.
How much extra should I add for waste?
About 10% for a simple gable roof, and up to 15% for roofs with many hips, valleys or dormers where more cuts are needed.