Roofing Calculator
Roof area, roofing squares and shingle bundles from the house footprint and roof pitch.
- Footprint area (sq ft)1,200
- Roof surface with 10% waste (sq ft)1,476
- Roofing squares14.8
- Shingle bundles (3 per square)45
Inputs used
- Footprint length40 ft
- Footprint width30 ft
- Roof pitch6/12 — average
About this calculator
A pitched roof is bigger than the footprint beneath it: the pitch multiplier converts flat area to true roof surface. A 6/12 pitch (6 inches of rise per foot of run) multiplies the footprint by about 1.118, so a 40 × 30 house carries roughly 1,342 square feet of actual roof.
Roofers measure in "squares" — one square is 100 square feet — and standard architectural shingles come three bundles to the square. The bundle count below already includes 10% for waste: ridge caps, valleys and cut-offs at edges consume more than flat math suggests, and complex roofs with many hips and valleys can need 15%.
Enter the footprint (the area the roof covers when viewed from above), not the wall dimensions — include eave overhangs, which typically add a foot or two on each side.
Results are informational only — not financial, medical or legal advice.