How it is calculated
Each roof plane is its eave length times its rafter length. Rafter length is the horizontal run plus overhang divided by the cosine of the pitch angle. For a hip roof with equal pitches, the area equals the plan area with overhangs divided by the same cosine. Shingles come three bundles per square (100 sq ft).
Pitch factor = √(12² + rise²) ÷ 12Roof area = plan area with overhangs × pitch factorBundles = roof area ÷ 33.3 sq ft × (1 + waste)Example
A gable roof on a 40 × 30 ft house with a 6/12 pitch and 1 ft overhangs covers 1,503 sq ft, about 15 squares. That takes 50 bundles of shingles with 10 % waste, 50 sheets of 4 × 8 OSB and 2 rolls of 1,000 sq ft underlayment. The ridge sits 7.5 ft above the walls.
Tips from practice
- Add more waste for hips and valleys: 15 % is common on complex roofs.
- Starter strip and ridge cap are sold separately; ridge cap covers about 20–33 linear feet per bundle.
- Check the minimum pitch for your shingles, usually 2/12 with special underlayment and 4/12 normally.
Questions and answers
How many bundles of shingles in a square?
Three bundles of standard architectural shingles cover one square, 100 sq ft.
What does 6/12 pitch mean?
The roof rises 6 in for every 12 in of horizontal run, about 26.6°.
How many squares is a 2,000 sq ft house roof?
It depends on pitch and overhangs; a 6/12 gable roof on a 2,000 sq ft footprint is roughly 23–24 squares.
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