Roofing materials · Updated November 3, 2026
Roof underlayment roll estimator
Estimate whole roof underlayment rolls from measured roof-face area and the selected product's net roll coverage after required laps.
Estimate whole underlayment rolls from measured roof-face area and the net coverage listed for your selected roll after its required laps. Enter the installed coverage, not gross roll dimensions. The calculation runs in your browser.
Enter values and calculate.
Need sloped roof-face area from plan dimensions? Use the roof pitch area calculator for rectangular planes, then add the measured roof faces that will receive underlayment.
How to estimate underlayment rolls
- Measure and add the roof-face areas that will receive the selected underlayment.
- Read the selected product's net coverage per roll when installed according to its current instructions. Account for side and end laps in that coverage value.
- Divide the measured roof area by net coverage per roll and round up to a whole roll.
The result is a basic area estimate. This calculator does not add a waste allowance, estimate ice-barrier placement, decide which underlayment suits a roof, or determine code requirements. Measure separate roof sections carefully and verify quantities, laps, compatibility and local requirements against the chosen product instructions and local building authority.
Sources and method
- TAMKO Specialty Underlayments (accessed November 3, 2026): links each listed product to its own data sheet and application instructions; products have distinct characteristics and requirements.
- TAMKO TW Underlayment Application Instructions (revised February 21, 2020; accessed November 3, 2026): for this specific product, the instructions describe 4-inch edge laps and 6-inch end laps. Those dimensions are not applied as a universal rule here.
Formula: whole rolls = ceil(measured roof-face area ÷ selected product net coverage per roll after laps). Use the coverage applicable to the exact product and installation method. Roll dimensions or gross material area are not interchangeable with installed net coverage.
How it works
Measure the roof faces that will receive underlayment and enter the selected product's net area coverage per roll after its specified laps. The estimator divides area by coverage and rounds up to whole rolls; it does not add an allowance or determine installation and code requirements.
Good to know
Quick answer: how many underlayment rolls do I need?
Divide the measured roof-face area by the selected product's net coverage per roll after required laps, then round up to a whole roll. Read net coverage and installation requirements for the exact product and application. Reviewed November 3, 2026.
What coverage should I enter?
Use the installed net coverage for the exact roll and installation method, accounting for required side and end laps. Do not use gross roll dimensions as though every square foot remains exposed after overlap. Product data sheets and instructions may state coverage differently, so confirm what the figure represents.
Are lap dimensions the same for every underlayment?
No. Follow the current instructions for the selected product and application. TAMKO's TW Underlayment instructions, for example, describe 4-inch edge laps and 6-inch end laps for that product; this estimator does not apply those dimensions to other products.
Does the estimate include an allowance or code requirements?
No. It divides measured area by your entered net roll coverage and rounds up. It does not add a waste allowance, determine ice-barrier placement, choose a suitable product or determine local code requirements. Verify the project with the selected product instructions and local building authority.
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