CALCULATORROOFING-UNDERLAYMENT-CALCULATOCALCULATE · DECIDE · ACT
Roofing Calculators · reviewed September 1, 2026
Roofing Underlayment Calculator
Estimate roofing underlayment rolls from roof area, waste, and the actual square-foot coverage printed on your roll.
Ready.
Enter your measurements and calculate.
Enter your measurements and calculate.
Worked example
Example
A 1,500 sq ft roof with 10% allowance requires 1,650 sq ft of coverage. A 1,000 sq ft roll means two rolls.
References
Sources & assumptions
Last reviewed September 1, 2026. Defaults are starting points; product-specific inputs are editable wherever coverage varies.
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FAQ
Common questions
Do all rolls cover the same area?
No. Felt and synthetic products have different sizes and effective coverage.
Should I use roof area before or after waste?
Use an allowance that accounts for laps, cuts, and the product installation pattern.
Does this include ice-and-water membrane?
No. Treat that as a separate membrane quantity.