How to use the Roofing Calculator
The roofing calculator estimates roof area, squares and shingle bundles.
What you need to enter
- Building length (ft)
- Building width (ft)
- Pitch (rise per 12)
- Overhang (ft)
- Waste (%)
The formula
Roof area ≈ (length + 2 × overhang) × (width + 2 × overhang) × √(1 + (pitch ÷ 12)²). One square = 100 sq ft.
Worked example
Using the default values in the calculator:
- Building length (ft): 40
- Building width (ft): 30
- Pitch (rise per 12): 6
- Overhang (ft): 1
- Waste (%): 10
| Roof area | 1,503 sq ft |
| Roofing squares (with waste) | 16.5 |
| Shingle bundles (3 per square) | 50 |
Tips for better results
- Add 10% waste.
- Complex roofs need more.
Common mistakes to avoid
- Using the floor area.
- Forgetting waste.
Please note: Results are estimates for general use. For safety-critical work such as electrical or building projects, check with a qualified professional and local codes. See our Disclaimer.