Roofing Calculator (Squares, Bundles & Pitch Factor)
Roof area from the house footprint and pitch, converted to roofing squares (100 sq ft) and shingle bundles.
Formula
Pitch factor = √(1 + (rise/12)²). Roof area = (L + 2×overhang) × (W + 2×overhang) × pitch factor. Squares = area ÷ 100 × (1 + waste%).
Worked example
Inputs: Footprint length = 40 ft; Footprint width = 30 ft; Eave/rake overhang = 12 in; Pitch (rise per 12 in run) = 6 in; Waste allowance = 10 %; Bundles per square (see wrapper) = 3.
| Pitch factor | 1.118 |
|---|---|
| Roof area sq ft | 1,502.64 |
| Squares | 16.53 |
| Bundles | 50 |
FAQ
What is a roofing square?
100 square feet of roof surface.
How many bundles per square?
Check the shingle wrapper; many standard shingles are packaged at 3 bundles per square, but some products differ.
Does this work for complex roofs?
It assumes a simple gable/hip with uniform pitch. Valleys, dormers and multiple pitches need extra waste or a measured takeoff.
Sources
- Geometry (volume/area formulas); no external constant needed
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Last reviewed 2026-10-11.