Roofing Calculator
No ladder needed — enter the building footprint and pitch, and get the sloped roof area in squares (100 ft²), shingle bundles, and #15 felt rolls, with ridge and edge lengths for trim takeoff.
How roof area is calculated
The pitch multiplier converts plan area to sloped area: √(12² + rise²) ÷ 12. A 6/12 pitch gives √180 ÷ 12 ≈ 1.118 — so the roof is 11.8% bigger than its footprint.
Worked example: 40 × 24 ft gable roof at 6/12 → 960 × 1.118 ≈ 1,073 ft² ≈ 10.7 squares → with 10% waste, order 12 squares (about 36 bundles).
Pitch multipliers
| Pitch | Multiplier | Pitch | Multiplier |
|---|---|---|---|
| 1/12 | 1.003 | 7/12 | 1.158 |
| 2/12 | 1.014 | 8/12 | 1.202 |
| 3/12 | 1.031 | 10/12 | 1.302 |
| 4/12 | 1.054 | 12/12 | 1.414 |
| 5/12 | 1.083 | 16/12 | 1.667 |
| 6/12 | 1.118 | 18/12 | 1.803 |
Coverage quick facts
- 1 square = 100 ft² of roof = 3 bundles of standard shingles
- #15 felt: ~4 squares per roll with typical laps
- Drip edge: total eave + rake lengths
Frequently asked questions
- How do I measure pitch without getting on the roof?
- Hold a level against the underside of a rafter in the attic: 12" out, measure up. Or count courses of siding between floor and eave. Enter the rise per 12" here.
- How much waste should I add?
- 10% for simple gable roofs, up to 15% for hips and valleys, more on cut-up roofs with dormers. Bundles round up automatically.