Use this free roof felt underlayment calculator to get instant, accurate results for your construction project. Simply enter your measurements above and the calculator will automatically compute the result using industry-standard formulas.
Pro Tip: Always add 10-15% extra material to account for waste, cuts, and job-site conditions. This is standard practice recommended by experienced contractors.
| Pitch | Multiplier | Extra % |
|---|---|---|
| 3/12 | ×1.031 | +3.1% |
| 4/12 | ×1.054 | +5.4% |
| 6/12 | ×1.118 | +11.8% |
| 8/12 | ×1.202 | +20.2% |
| 12/12 | ×1.414 | +41.4% |