How this roofing underlayment calculator works
Roof area is increased for overlaps and waste, then divided by effective roll coverage.
How to use it
- Roof surface area. Enter the value in sq ft.
- Effective coverage per roll. Enter the value in sq ft.
- Overlap/waste allowance. Enter the value in %.
- Request the result. Add your email, then select “Email & show my result.”
What to do with the number
Valleys, hips, laps and membrane-specific installation details can increase material use. Use effective rather than nominal roll coverage if the manufacturer publishes both.
Planning estimate
Use this result as a starting point, not a guarantee. Product specifications, site conditions, manufacturer guidance, local codes, taxes, labor, tolerances, and rounding can change the real requirement or cost.