Roofing Calculator
Calculate roof area, roofing squares (100 sq ft), and shingle bundles from plan size, pitch, sections, and waste. Optional cost per square.
How to use this roofing calculator
Roofers bid in squares: 1 roofing square = 100 square feet of roof surface, not floor area. A 6:12 pitch is steeper than the footprint, so you multiply plan area by the pitch factor √(1+(6/12)²) ≈ 1.118. Simple gables are two rectangles; add sections for an L-shaped house.
Three bundles per square is the common asphalt-shingle packing. Architectural shingles can differ — check the wrapper. Valleys, hips, and starter strip eat extra; 10–15% waste is the usual carton. This roofing calculator does not replace a measured takeoff on a complex roof. Use the Roof Pitch Calculator if you only have rise and run.
Formula
Worked example
Two 40×24 ft rectangles, 6:12 pitch, 10% waste: plan 1,920 sq ft × 1.118 = 2,147 sq ft × 1.10 = 2,361 sq ft = 23.6 squares ≈ 71 bundles.
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Frequently asked questions
What is a roofing square?
100 square feet of roof area. Ten squares is 1,000 sq ft of shingles, not a 10×10 bedroom.
How do I calculate roof square footage?
Measure each rectangle of the floor plan the roof covers, multiply by the pitch factor, and add waste. This tool does that from length, width, pitch, and section count.
How many shingle bundles per square?
Usually three bundles per square for asphalt. Confirm on the bundle label.
How does roof pitch change materials?
Steeper pitch means more area for the same house footprint. A 12:12 roof has a pitch factor of 1.414 — about 41% more shingles than a flat plan.
What waste percent for roofing?
10% on a simple gable. 15% with hips, valleys, and dormers.
Results are estimates for informational purposes and are not financial, legal, or professional advice. Last reviewed 2026-08-19.