Roof Underlayment Calculator
Enter your size to get roof underlayment quantity, plus an estimated cost. Waste is included and prices are editable.
Material needed
Estimated cost
How to calculate roof underlayment
Roof underlayment sold by the square foot. Enter roof area to get square feet.
Formula: quantity = area × 1 × (1 + waste %) = 100 × 1 × 1.10 = 110 sq ft.
Worked example
Example: 10 ft × 10 ft = 100 sq ft. Quantity: 110 sq ft, about $55 at $0.5 per sq ft.
Tips
Measure the full area, then subtract large openings if you want an exact count. Order a little extra for cuts and breakage, and confirm quantities with your supplier before you buy.
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Frequently asked questions
How much roof underlayment do I need?
Example: 10 ft × 10 ft = 100 sq ft. Quantity: 110 sq ft, about $55 at $0.5 per sq ft.
How much waste should I add?
Add 10% for straight areas and 15% for areas with many cuts, corners and openings.
Are the prices accurate?
Prices are editable estimates. The defaults are typical US figures, and your local price can be higher or lower.