Flooring Underlayment Calculator
Calculate how many 100 sq ft rolls of foam flooring underlayment you need from your room's area, plus total cost.
How this calculator works
Foam flooring underlayment is sold in rolls that cover a fixed area — 100 square feet is the common roll size. This calculator divides your room’s area by that coverage and rounds up to a whole roll.
Formula: Rolls = Room area (sq ft) ÷ 100 sq ft per roll, rounded up.
Worked example
A room 15 ft long x 12 ft wide (180 sq ft):
- Area: 15 x 12 = 180 sq ft
- Rolls: 180 ÷ 100 ≈ 1.8 → rounds up to 2 rolls
- At $30/roll, that’s 2 × 30 = $60.00.
Coverage reference
| Room area | Rolls needed (100 sq ft/roll) |
|---|---|
| 45 sq ft | 1 rolls |
| 180 sq ft | 2 rolls |
| 720 sq ft | 8 rolls |
How to measure your room
Measure the room’s length and width in feet, covering the full floor area that will receive new flooring, including closets that will be floored to match. Skip this calculator entirely if you’re installing attached-pad luxury vinyl plank, since a second underlayment layer isn’t needed and may not be recommended by the manufacturer.
Frequently asked questions
What size does underlayment come in?
This calculator assumes a standard 100 sq ft roll of foam underlayment, one of the most common roll sizes sold at flooring retailers. Some brands package rolls at 200 sq ft or more, so check your specific product before ordering.
Do I need underlayment under every floor type?
It depends on the plank. Laminate and standard vinyl plank almost always call for a separate foam underlayment for sound dampening and minor subfloor leveling. Attached-pad luxury vinyl plank (LVP) already has a foam layer bonded to the back, so adding a second underlayment layer can actually void the warranty or create a spongy feel underfoot.
How do I know if my plank has attached pad?
Check the product spec sheet or flip a sample plank over — attached-pad planks have a visible foam or cork layer laminated to the back. If you can't tell, contact the manufacturer, since installing over the wrong underlayment combination is a common cause of warranty denial.
Why isn't a waste allowance included here?
Underlayment rolls unroll in long continuous sheets and seams just butt together rather than needing mitered cuts, so waste is minimal on a simple rectangular room. This calculator already rounds up to the next full roll, which typically covers minor trim waste.
Estimates only. Verify quantities with your supplier before purchasing.