How roof area is calculated
A sloped roof has more surface than the ground it covers. Multiply the footprint, including the overhang, by a pitch multiplier. This works for gable and hip roofs alike, as long as every plane has the same pitch.
Example: a 40 × 30 ft house with a 12" overhang has a 42 × 32 ft footprint, or 1,344 sq ft. A 6/12 pitch multiplies that by 1.118, giving 1,503 sq ft of roof: 15.03 squares, or 16.53 with 10% waste. That's 50 bundles of shingles.
Pitch multipliers
| Pitch | Multiplier | Angle |
|---|---|---|
| 3/12 | 1.031 | 14.0° |
| 4/12 | 1.054 | 18.4° |
| 5/12 | 1.083 | 22.6° |
| 6/12 | 1.118 | 26.6° |
| 7/12 | 1.158 | 30.3° |
| 8/12 | 1.202 | 33.7° |
| 9/12 | 1.250 | 36.9° |
| 10/12 | 1.302 | 39.8° |
| 12/12 | 1.414 | 45.0° |
Most architectural shingles come 3 bundles to a square; some heavy designer shingles take 4 or 5. Ridge cap, starter strip and nails are bought separately. Measure flat areas with the square footage calculator.
Frequently asked questions
How many bundles of shingles do I need?
Three bundles per roofing square (100 sq ft) for standard architectural shingles, plus 10% to 15% waste. A 2,000 sq ft roof needs about 66 to 69 bundles.
What is a roofing square?
100 square feet of roof surface. Roofers price jobs and order materials by the square.
How do I find my roof pitch?
Hold a level horizontally against the roof, measure 12 inches along it, then measure straight up to the roof surface. That rise in inches is the pitch: 6 inches means 6/12.
Was this calculator helpful?