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Materials & Projects

Roofing Underlayment Calculator

Enter the building footprint and roof pitch so the calculator can estimate sloped roof area. This avoids needing to measure or calculate the roof surface area first.

Last updated: July 2026

Unit system Switch between U.S. customary and metric units. Your choice is remembered on other calculators.

Building footprint and roof pitch

Use the building footprint or roof plan dimensions. Pitch is entered as rise per 12 inches of run, such as 6 for a 6/12 roof.

Visual guide

Which measurement goes where?

Use building footprint and roof pitch. The roll count then uses estimated sloped roof area and the roll coverage you enter.

ft
ft
per 12 in run
Enter 6 for a 6/12 roof, 8 for an 8/12 roof, etc. This is treated as a pitch ratio, not a length to convert.
sq ft/roll
Advanced settings
ft each side
Adds this amount to each side of the roof plan footprint. Set to 0 if your dimensions already include overhangs.
sq ft
Add extra surface area for dormers, porch roofs, additions, or sections not included in the main footprint.
%

Buying and sizing notes

How to use this estimate

What this includes

  • The required inputs shown on this page
  • common planning assumptions
  • optional advanced adjustments where provided

What it does not include

  • site-specific professional design
  • local code approval
  • manufacturer-specific requirements
  • installation quality

Common mistakes

  • Leaving a required input at the default when your situation is different
  • ignoring product labels or ratings
  • treating the estimate as an exact final answer

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