Roof Square Footage Calculator
Calculate roof area, convert to roofing squares (1 square = 100 sq ft), and estimate the number of shingle bundles you'll need to order.
Roof Calculator
Footprint vs. actual roof area
A common mistake is measuring the building's footprint (the ground area it covers) and using that for roof estimates. Roofs slope, so the actual surface area is always larger than the footprint.
For a typical 4/12 pitch roof, multiply footprint by 1.06. For a 6/12, multiply by 1.12. For 8/12, multiply by 1.20. Steeper roofs grow even more relative to footprint — and require steep-slope premium pricing from contractors.
Roofing squares & shingle bundles
In roofing, a "square" equals 100 square feet. So a 2,400 sq ft roof is 24 squares. Most asphalt shingles are sold in bundles, with 3 bundles per square — meaning that 24-square roof needs 72 bundles.
Add 10% for waste from hips, valleys, ridge cap, starter strips, and offcuts. Steep roofs and complex roofs with many planes need 15%.
Pro tips
Use Google Maps for the footprint
If you can't safely measure, satellite imagery and Google Maps measuring tools give a close estimate of your roof footprint.
Don't forget overhangs
Most roofs overhang the walls by 12–24 inches. Measure the actual roof line, not just the building.
Account for ridge cap
Ridge cap shingles are sold separately from field shingles. Calculate ridge length × 1 ft for ridge cap area.
Two layers? Double up
If you're doing a tear-off and overlay, you're only buying one layer. If you're going over an existing layer (where allowed), you only need one layer of new shingles.