Roof materials
Underlayment roll calculator
Estimate underlayment rolls. Shingle or metal roof material takeoff.
Try the calculation
Use product roll coverage after overlaps.
Adjustable example. Change these illustrative inputs to match your task, then recalculate. Reset restores the example and its result.
Understand the result
How this calculation works
Underlayment roll count depends on effective roll coverage after overlaps.
Steps
- Enter roof area, roll coverage and a waste percentage from your takeoff.
- Use the product coverage consistently.
The form starts with the worked example below. Change its values and selections to match your task; Reset restores the example.
Formula
rolls = ceiling(area × (1 + waste ÷ 100) ÷ roll coverage).
Variables and units
- Roof area (sq ft)
- Required. Use a positive value. Starting example: 1500. Replace it for your task.
- Roll coverage (sq ft)
- Required. Use a positive value. Starting example: 1000. Replace it for your task.
- Waste allowance (%)
- Required. Zero is accepted. Starting example: 10. Replace it for your task.
What the result means
The result is a rounded roll count. It does not decide where underlayment is required.
Worked example
Inputs: Roof area = 1500; Roll coverage = 1000; Waste allowance = 10.
Calculation: 1,500 sq ft with 10% waste and 1,000 sq ft per roll: 1,650 ÷ 1,000 = 1.65, so 2 rolls.
Result: 2 rolls.
Frequently asked questions
Does this decide ice-and-water protection?
No. Protected areas use the separate barrier calculation.
Should roll overlap be included?
Use effective coverage after the product installation overlap.
Can I enter a zero waste allowance?
Yes, if that is the assumption you are checking.