Primary material
2 rolls
Underlayment rolls
Use the roll count as a buying starting point, then confirm the square feet per roll and the type your flooring calls for before ordering.
Flooring underlayment calculator
Flooring underlayment calculator for rolls, coverage, and cost.
Estimate underlayment rolls from room size, type, roll coverage, and overlap waste before buying foam, cork, felt, or rubber under laminate, vinyl plank, or engineered floors.
Quick reference
Underlayment rolls for common room sizes
100 sq ft rolls with the default 10% for overlap and trimming. Check the coverage printed on your roll.
| Room size | Floor area | With overlap | Rolls |
|---|---|---|---|
| 10 x 10 ft | 100 sq ft | 110 sq ft | 2 |
| 12 x 12 ft | 144 sq ft | 158 sq ft | 2 |
| 12 x 15 ft | 180 sq ft | 198 sq ft | 2 |
| 15 x 20 ft | 300 sq ft | 330 sq ft | 4 |
| 20 x 20 ft | 400 sq ft | 440 sq ft | 5 |
Run underlayment the same direction as the planks and tape the seams unless the product says to overlap.
Quick underlayment answers
Common room checks
12 x 12 bedroom
2 rolls
158 sq ft with waste
at 100 sq ft per roll
10 x 20 living room
3 rolls
220 sq ft with waste
at 100 sq ft per roll
20 x 30 main floor
7 rolls
660 sq ft with waste
at 100 sq ft per roll
Shopping list
Compare underlayment, vapor barrier, and seam tape
Moisture control
Vapor barrier or 2-in-1 underlayment
Floating floors over concrete usually need a moisture barrier. Some 2-in-1 and 3-in-1 underlayments build it in — check the flooring instructions.
Seams
Seam tape
Underlayment seams and vapor-barrier laps are taped so they stay closed during the install. Plan a roll or two per project.
Tools
Utility knife and straightedge
Rolling out underlayment cleanly needs a sharp utility knife, a straightedge, and the tape above. Cut it to fit walls and obstacles.
Formula shown
How underlayment estimates work
Room square footage
floor area = length x width + extra area
Overlap and cut waste
required area = floor area x (1 + waste allowance)
Roll count
rolls = ceil(required area / square feet per roll)
Type prices are typical retail material ranges and vary by brand and region: foam is the lowest cost, cork and felt sit higher, and rubber is the most expensive. They are estimates only — check the product label and your local price.
Sources
- The Home Depot underlayment buying guide — underlayment types, vapor barrier guidance, and roll coverage context
- Lowe's flooring underlayment guide — foam, cork, and felt underlayment types and where each is used
- The Home Depot square footage guide — length times width square-foot formula
Sources checked
Checked against
Box coverage, waste factors, and cost ranges checked against retailer calculators and published cost guides.
How we check our numbersLast updated: June 29, 2026
Estimate only.
This calculator is not a quote. Verify product yield, price, delivery minimums, and local conditions with your supplier or contractor before buying materials.
Waste area
14 sq ft waste
Overlap and cut allowance before roll round-up.
Coverage purchased
200 sq ft purchased
Whole rolls multiplied by roll coverage.
Extra after round-up
56 sq ft extra after round-up
Useful for closets, repairs, and overlap.
Related flooring calculators
Estimating the whole floor?
Underlayment is one layer. Use the boxes calculator for the flooring itself, the transition calculator for doorways and stairs, or the flooring cost calculator for an installed total.
FAQ
Flooring underlayment calculator questions
Quick answers for rolls, coverage, underlayment type, vapor barrier, and overlap waste.
How many rolls of underlayment do I need? + -
Measure the floor area, add a small overlap and cut allowance, then divide by the square feet covered by one roll and round up. Most foam and cork rolls cover about 100 sq ft, but rolls vary widely, so use the number printed on the product.
Do I need underlayment under my flooring? + -
It depends on the product. Many laminate and floating vinyl planks need a thin underlayment for sound and feel, while some planks include attached pad and need none. Over concrete you usually also need a moisture barrier. Always follow the flooring installation instructions.
What type of underlayment should I use? + -
Foam is the common, low-cost choice for laminate and floating LVP. Cork adds sound control and a firmer feel. Felt is dense and quiet. Over concrete, choose a product with a built-in vapor barrier or add a separate 6-mil barrier. Match the type to your subfloor and flooring.
Should underlayment overlap or butt together? + -
Most foam and cork underlayment butts edge to edge and is seam-taped, while attached or filmed products lap the film flap over the next row. The small waste allowance in this calculator covers the laps and wall cuts.
Can I use underlayment over an attached pad? + -
Usually no. Adding a second pad under a plank that already has attached underlayment can void the warranty and make the floor feel spongy. Check the manufacturer instructions before doubling up.