Roofing Underlayment Calculator
Estimate roofing-underlayment rolls, effective coverage, total order area, lap allowance and material cost for a simple gable roof.
Default project preview
5 rolls
Roof surface area
1,421 ft²
Order area
1,563.1 ft²
Effective roll coverage
368 ft²
Purchased coverage
2,000 ft²
Calculator
Build the material order
Your order will appear here
Enter the project details and calculate a rounded material estimate.
Methodology
Transparent calculation
BuildMeter converts every input to a consistent internal unit, applies the selected allowance, and rounds products up to whole purchasable units.
Roof surface uses the pitch slope factor. Effective roll coverage = published coverage × (1 − lap loss). Rolls = round up (roof order area ÷ effective coverage).
BuildMeter Guides
Understand the measurements and assumptions
Use these visible reference guides before changing project inputs or planning allowances.
FAQ
Roofing Underlayment Calculator questions
Does roll coverage already include overlaps?+
Some manufacturers publish effective coverage and others publish gross roll area. Check the product data before adding a lap-loss factor.
Is ice-and-water membrane included?+
No. Eaves, valleys and penetrations may require separate membrane quantities.
Can the same underlayment be used under every roof covering?+
No. Compatibility and fastening requirements depend on the roof covering and assembly.