Roof underlay calculator
Estimate underlay rolls with side-lap allowance.
Your measurements
Enter your project values. Your estimate updates as you type.
View your estimateExample values are a starting point. Check product yields and specifications before ordering.
YOUR ESTIMATE
Rolls to buy
Whole quantities are rounded up.
How it's calculated
Effective roll area = (roll width − side overlap) × roll length. Rolls = area with waste ÷ effective coverage, rounded up.
Calculations use consistent units for your selected measurements. The waste allowance is applied once to the measured requirement. Whole purchase quantities are rounded up.
What this estimate includes
Enter the sloping roof area. End laps and complex cuts are covered only by your chosen waste allowance.
Quantity and arithmetic estimates only. Use project specifications for installation and design requirements.