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Flooring & TileFloor Underlayment Calculator — How Many Rolls Do I Need?
Enter your room’s length and width to find how much floor underlayment you need — the number of rolls to buy for a laminate or engineered floating floor, based on about 100 sq ft per standard foam roll. Roll sizes vary, so confirm the coverage printed on yours.
How this calculator works
We take the room area, add 5% for overlap and trimming, and divide by about 100 sq ft per roll — a common foam-underlayment size. Cork, felt, and premium rolls differ, so check your product.
What changes how much you need
- Roll coverage varies a lot — standard foam is ~100 sq ft, but others differ; check the label.
- Many click-lock floors come with attached padding and need no separate underlayment.
- Overlap or butt seams exactly as the instructions say, and tape them.
- Over concrete, use an underlayment with a built-in moisture barrier (or add one).
Underlayment rolls by room size (100 sq ft foam rolls)
| Room | Area | Rolls to buy |
|---|---|---|
| Small bedroom · 10 × 10 ft | 100 sq ft | 2 rolls |
| Bedroom · 12 × 12 ft | 144 sq ft | 2 rolls |
| Large bedroom · 12 × 15 ft | 180 sq ft | 2 rolls |
| Living room · 15 × 20 ft | 300 sq ft | 4 rolls |
| Great room · 20 × 25 ft | 500 sq ft | 6 rolls |
Frequently asked questions
How many square feet are in a roll of underlayment?
Often about 100 sq ft for standard foam, but premium, cork, and felt rolls vary — read the packaging.
Do I need underlayment under laminate?
Usually yes, unless the planks already have attached padding. It cushions, quiets, and evens out minor subfloor imperfections.
Do I need a moisture barrier?
Over concrete or below grade, yes. Use underlayment with a built-in vapor barrier or lay one first.
How much underlayment do I need for a 12×12 room?
A 12×12 room is 144 sq ft. Adding about 5% for overlap and trimming brings it to roughly 151 sq ft, so you’d buy 2 standard 100 sq ft rolls. Enter your exact dimensions above for any room size.
How much extra underlayment should I buy for waste?
About 5% for overlap and trimming — this calculator already includes it. For rooms with lots of cuts (closets, angles, or diagonal layouts), bump it to 10%.
How much does floor underlayment cost?
Basic foam runs about $0.30–$0.50 per sq ft, so a 144 sq ft room is roughly $45–$75. Cork, felt, and combination moisture-barrier underlayments cost more (about $0.50–$1.00+ per sq ft). Multiply your room area by the per-sq-ft price for a quick material budget.