A roofing square = 100 square feet of roof area. Roofers use this unit to price materials and labor consistently.
How to Calculate
1. Measure roof footprint (length × width)
2. Multiply by pitch factor (e.g., 4/12 pitch = ×1.054, 6/12 = ×1.118, 8/12 = ×1.202)
3. Divide total sq ft by 100 = number of squares
Materials per Square
- 3-tab shingles: 3 bundles per square
- Architectural shingles: 3–4 bundles per square
- Underlayment: 1 roll per 2–4 squares
Why Pitch Increases Material Needed
A steeper roof has more actual surface area than its "footprint" (the flat area visible from directly above) suggests — a 12/12 pitch (45°) roof has about 41% more surface area than the flat footprint measurement, which is why the pitch multiplier step in the calculation isn't optional for accurate material ordering.
Waste Factor
Simple rectangular roofs need only 10% extra material for waste and cuts; complex roofs with many valleys, hips, and dormers can require 15–20% extra due to the additional cutting and fitting around each roof feature — a factor often underestimated in DIY material estimates.