Roofing Calculator
Estimate roof area from the building footprint, roof pitch and overhang, then find how many roofing squares and shingle bundles to buy.
How roof area is estimated
Roof area = footprint (with overhang) × pitch factor Pitch factor = √(1 + (rise ÷ 12)²) Squares = roof area ÷ 100
One roofing square covers 100 sq ft. Most architectural asphalt shingles come 3 bundles to a square, but check the package.
Worked example
A 50 × 30 ft house with 12 in overhangs has a 52 × 32 = 1,664 sq ft footprint. A 6/12 pitch has a factor of 1.118, so the roof is about 1,860 sq ft. With 10% waste that is 20.5 squares, or 62 bundles.
Pitch factors
| Pitch | Factor | Pitch | Factor |
|---|---|---|---|
| 3/12 | 1.031 | 8/12 | 1.202 |
| 4/12 | 1.054 | 9/12 | 1.250 |
| 5/12 | 1.083 | 10/12 | 1.302 |
| 6/12 | 1.118 | 12/12 | 1.414 |
This works for simple gable and hip roofs. Dormers, valleys and multiple levels need more material; get a professional measurement for complex roofs.
Frequently asked questions
What is a roofing square?
100 square feet of roof area.
How many bundles of shingles in a square?
Usually 3 for standard architectural shingles; some heavier products use 4 or 5.
How do I find my roof pitch?
Measure how many inches the roof rises over 12 inches of horizontal run.
Should I include starter and ridge shingles?
They are usually bought separately, based on the length of eaves, rakes and ridges.
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