What is a roofing square?
A 'square' is the roofing trade's unit for 100 square feet of roof area. Roofers, estimates, and shingle packaging all measure in squares, and most shingles run about 3 bundles per square. It's an industry convention for estimating and ordering — not a building-code value.
Source: Roofing trade convention (not a code value) · Verify against your AHJ and the adopted code edition.
A roofing square equals 100 square feet of roof surface. It’s the unit the whole trade estimates and orders in: shingles are sold and bundled by the square, and a roofer will quote “22 squares,” not “2,200 square feet.”
Two things trip people up:
- Roof area is bigger than the footprint. A pitched roof covers more surface than the plan area beneath it. You multiply the footprint by a slope factor (√(rise² + 12²) ⁄ 12) to get the true roof area before converting to squares.
- Bundles per square vary. Most three-tab and architectural shingles run about 3 bundles per square, but heavier products differ — always check the wrapper for the exact coverage.
Order a little extra, too: 5–15% waste is typical for cuts, starter courses, and hip/ridge caps.
Work it out: the roofing calculator takes a footprint and a pitch, applies the slope factor, and returns the roof area in square feet and squares plus an estimated bundle count with a waste allowance.