Free visual roofing tools
Roof Underlayment Calculator
Turn sloped roof area into whole rolls using the product’s usable coverage.
Whole rolls for this scenario
5 rollsWHOLE ROLLS · ROUNDED UP
Each symbol represents up to 1 rolls.
0 sq ft beyond scenario coverage after rounding.
- Net sloped area
- 2,000 sq ft
- Added allowance (0%)
- 0 sq ft
- Scenario coverage needed
- 2,000 sq ft
- Coverage after rounding up
- 2,000 sq ft
Enter usable coverage after the product’s required overlaps. Do not deduct overlaps again. Round up only after adding your allowance. Confirm layout and product instructions before ordering.
Display rounded to 2–4 decimals; calculations keep full precision. Whole purchase units round up.
Rolls = round up (scenario area ÷ usable coverage per roll)
Educational planning tool · Example values are not measurements of your property.
Use coverage after overlaps
Rolls = round up [net sloped area × (1 + waste percentage ÷ 100) ÷ usable coverage per roll]. Use coverage after required overlaps from your selected product’s instructions. Do not deduct those overlaps twice.
A worked example
For a synthetic 2,000 sq ft roof, a chosen 10% allowance gives 2,200 sq ft. At an example usable coverage of 400 sq ft per roll, this requires 5.5 rolls, rounded upward to 6 whole rolls. Those rolls provide 2,400 sq ft of usable coverage.
| Scenario area | Usable coverage per roll | Whole rolls |
|---|---|---|
| 2,200 sq ft | 400 sq ft | 6 |
A planning quantity, with assumptions
The 400 sq ft default is an illustration, not a manufacturer specification. Layout, cuts, multiple layers and product-specific installation requirements may change quantities. Ice-and-water membrane and other accessories are separate.