Roofing Calculator
Estimate roof area from the house footprint and pitch, plus shingle squares and bundles.
About the Roofing Calculator
Roof area is the footprint (including overhangs) multiplied by the pitch factor √(1 + (rise ÷ run)²). Roofers measure in squares of 100 ft²; standard shingles come 3 bundles to the square. Add 10% waste for a simple gable roof and 15% or more for hips and valleys.
The formula
Roof area = footprint × √(1 + (pitch ÷ 12)²)
Pitch factors
| Pitch | Angle | Factor |
|---|---|---|
| 3/12 | 14° | 1.031 |
| 4/12 | 18.4° | 1.054 |
| 6/12 | 26.6° | 1.118 |
| 8/12 | 33.7° | 1.202 |
| 10/12 | 39.8° | 1.302 |
| 12/12 | 45° | 1.414 |
Worked example
Example: Roof area = 1,681 ft²
- Inputs: Units: Imperial (ft, in); House length (incl. overhang): 44 ft; House width (incl. overhang): 33 ft; Roof pitch: 7 in 12; Waste: 11%.
- Formula: Roof area = footprint × √(1 + (pitch ÷ 12)²)
- Result: Roof area = 1,681 ft²
- Footprint: 1,452 ft²
- Squares: 18.7
- Shingle bundles: 56
Questions people ask
Does this work for hip roofs?
Yes, for the main area when all planes share one pitch; add more waste.
What's a roofing square?
100 square feet (9.29 m²) of roof.