Roofing Calculator
Estimate your roof’s surface area from the building footprint and roof pitch, then see approximate roofing “squares” and shingle bundles (including waste).
| House length | |
| House width | |
| Roof pitch | |
| Waste/overlap |
Estimate
Your roofing estimate will appear here.
Formulas and assumptions
- Pitch multiplier = √(rise² + 12²) / 12. For example, a 4:12 pitch has multiplier √(4²+12²)/12 ≈ 1.0541.
- Roof area ≈ footprint area × pitch multiplier (simple gable assumption, no overhangs/dormers/valleys counted separately).
- 1 roofing square = 100 sq ft of roof area. Asphalt shingles are often about 3 bundles per square (varies by product).
- Waste/overlap is added for cuts, hips, valleys, and starter/ridge pieces — complex roofs usually need more.
This is a planning estimate only. Actual materials depend on roof shape, overhangs, local codes, and the specific product — confirm with measurements and your supplier or contractor.
How it works
Roofing material is estimated from the footprint and pitch (slope), which increases surface area versus a flat footprint.
Formula and steps
- Pitch multiplier ≈ √(rise² + run²) / run. Roof area ≈ footprint × multiplier. Squares = area ÷ 100. Bundles vary by product (often ~3 per square) plus waste.
Worked example
30×40 ft at 6/12 pitch: ~1342 ft² ≈ 13.4 squares.
Estimate only. Actual material needs vary by roof complexity, waste, and local practice. Confirm with your supplier or roofer.
How to use the Roofing Calculator
It takes a few seconds, and every figure is calculated in your browser.
- Enter the house length.
- Enter the house width.
- Enter the roof pitch.
- Enter the waste/overlap.
- Press Calculate — the result appears in the dark panel beside the form.
- Use Copy, CSV, Share or Print under the result if you want to keep it.
Roofing Calculator — frequently asked questions
What formula does the Roofing Calculator use?
Pitch multiplier = √(rise² + 12²) / 12. For example, a 4:12 pitch has multiplier √(4²+12²)/12 ≈ 1.0541. Roof area ≈ footprint area × pitch multiplier (simple gable assumption, no overhangs/dormers/valleys counted separately). 1 roofing square = 100 sq ft of roof area. Asphalt shingles are often about 3 bundles per square (varies by product). Waste/overlap is added for cuts, hips, valleys, and starter/ridge pieces — complex roofs usually need more. This is a planning estimate only.
How does the Roofing Calculator work?
Roofing material is estimated from the footprint and pitch (slope), which increases surface area versus a flat footprint.
Can you walk through a worked example?
30×40 ft at 6/12 pitch: ~1342 ft² ≈ 13.4 squares.
Last updated 10 November 2026 · Formula, worked example and assumptions are documented above, and every result is calculated in your browser.