Underlayment Calculator
Figure out how much underlayment to buy for any floor — foam, cork, rosin paper, vapor barrier, plywood panels, or cement backer board — with rolls or sheets, fasteners, U.S. pricing, and a downloadable PDF material list.
Coverage varies by brand and thickness — always check the roll or sheet label. Match the underlayment to your finished floor and subfloor. For planning purposes only.
| Overage | Sq Ft to Buy | Rolls | Material Cost | Cost / sq ft |
|---|
For your 300 sq ft area. More overage = fewer short pieces but a little more spend.
How to use the underlayment calculator
Four quick steps turn your floor area into a full material list for any underlayment — rolls of foam, cork, felt, or poly, or sheets of plywood or cement backer board — with fasteners, U.S. pricing, and a downloadable PDF.
Enter the area
Length × width in feet, add closets and hallways, or type total square feet — or tap a preset like Living 15×20.
Pick the type
Foam, cork, felt, vapor barrier, plywood, or cement backer board — the calculator sets sensible defaults for each.
Set coverage, waste & prices
Confirm roll coverage or board size, set the waste %, and enter underlayment, fastener, and labor prices.
Read results & save a PDF
Get rolls or sheets, fasteners and accessories, a full cost breakdown, an overage comparison, and a material list.
How the underlayment estimate is calculated
It all starts from your floor area and waste allowance. From there the math forks by form: roll goods are counted by coverage, sheet goods by panel size, and sheet types add their own fasteners and bond materials. Here is the exact math behind each output.
Worked example — a 15 ft × 20 ft living room in foam underlayment
Net area: 15 × 20 = 300 sq ft
Buy area (+10%): 300 × 1.10 = 330 sq ft
Rolls: 330 ÷ 100 = 3.3 → 4 rolls
Square yards: 330 ÷ 9 = 36.7 sq yd | Foam cost: 330 × $0.40 = $132
≈ 4 foam rolls (330 sq ft), about $132 in underlayment at $0.40 / sq ft.
Underlayment estimating charts
Handy lookups for the questions people ask most — which underlayment suits which floor, rolls and sheets by area, and typical U.S. costs. Figures use the calculator’s defaults, so always confirm your own roll label or sheet size.
| Type | Form | Best for | Typical coverage | Typical U.S. price |
|---|---|---|---|---|
| Foam / cushion | Roll | Floating laminate & LVP | ~100 sq ft/roll | $0.30–$0.60 / sq ft |
| Cork | Roll | Sound & thermal under laminate, wood, tile | ~100 sq ft/roll | $0.60–$1.20 / sq ft |
| Felt / rosin paper | Roll | Slip sheet under nail-down solid wood | ~500 sq ft/roll | ~$0.10 / sq ft |
| Vapor barrier (6-mil poly) | Roll | Moisture control over concrete slabs | ~1,000 sq ft/roll | ~$0.06 / sq ft |
| Plywood / OSB panel | Sheet | Smoothing a rough subfloor | 4×8 = 32 sq ft | $25–$35 / sheet |
| Cement backer board | Sheet | Rigid base under tile | 3×5 = 15 sq ft | $12–$20 / sheet |
Match the underlayment to both the finished floor and the subfloor. Roll goods lay fast and cushion or block moisture; sheet goods rebuild the surface itself — plywood to smooth it, cement board to make it tile-ready.
| Area (+10% / +15%) | Foam / cork (100) | Felt (500) | Poly (1,000) |
|---|---|---|---|
| 100 sq ft | 2 rolls | 1 roll | 1 roll |
| 200 sq ft | 3 rolls | 1 roll | 1 roll |
| 300 sq ft | 4 rolls | 1 roll | 1 roll |
| 500 sq ft | 6 rolls | 2 rolls | 1 roll |
| 1,000 sq ft | 11 rolls | 3 rolls | 2 rolls |
Rolls = buy area ÷ roll coverage, rounded up. Foam and cork use +10% waste; poly uses +15% to cover 6–8″ overlapped seams. Coverage varies by brand, so set it from your label.
| Area | Plywood 4×8 (32) | Backer 4×8 (32) | Backer 3×5 (15) |
|---|---|---|---|
| 100 sq ft | 4 sheets | 4 sheets | 8 sheets |
| 200 sq ft | 7 sheets | 7 sheets | 15 sheets |
| 300 sq ft | 11 sheets | 11 sheets | 22 sheets |
| 500 sq ft | 18 sheets | 18 sheets | 37 sheets |
| 1,000 sq ft | 35 sheets | 35 sheets | 74 sheets |
Sheets = buy area ÷ sheet size, rounded up. Bigger boards mean fewer sheets and fewer seams. Backer board also needs thinset underneath (~45 sq ft per bag), screws on ~8″ centers, and taped seams.
| Line item | Typical U.S. range | What moves it |
|---|---|---|
| Foam underlayment | $0.30–$0.60 / sq ft | Thickness, attached film / vapor layer |
| Cork underlayment | $0.60–$1.20 / sq ft | Thickness, sound rating |
| Plywood / OSB panel | $25–$35 / 4×8 sheet | Thickness, grade, sheet size |
| Cement backer board | $12–$20 / sheet | 3×5 vs. 4×8, thickness (1/4″ vs 1/2″) |
| Fasteners & thinset | ~$10–$28 / box or bag | Staples, backer screws, bond coat |
| Professional install | set your own $/sq ft | Prep, type, layout — DIY = $0 |
2024–2025 U.S. ballparks matching the calculator’s defaults. Roll underlayment is cheap per square foot; cement-board tile prep costs more once screws, thinset, and tape are added. Your local quotes will vary.
foam · cork · felt · poly
4×8 panel
3×5 or 4×8
Underlayment comes in two forms. Roll goods unroll fast to cushion, quiet, or damp-proof a floor; sheet goods rebuild the surface you install on.
- Roll goods — foam & cork cushion floating floors, felt slips under nail-down wood, 6-mil poly blocks slab moisture.
- Plywood / OSB — 1/4″ panels smooth a rough subfloor before resilient or nail-down floors; stapled down.
- Cement backer — the rigid base under tile; set in thinset, screwed to a grid, and taped at the seams.
Everything the calculator works out
One floor area gives you a complete order for whichever underlayment you choose — the count in the right unit, plus the fasteners and bond materials that type needs.
Key figures every underlayment job depends on
Built for any underlayment job
From a foam roll under laminate to cement board under a tile floor, the same calculator scales to the type and the job.
Rolling foam or cork under a laminate or LVP floor and wants an exact roll count without over-buying.
- Start from a preset like Bedroom 10×12
- Check if the plank has an attached pad
- Don’t double up foam layers
Prepping a floor for tile and needs backer sheets, screws, thinset, and seam tape counted in one place.
- Pick the 3×5 or 4×8 board size
- Thinset goes under the board too
- Tape and screw every seam
Bidding floor prep across rooms and comparing underlayment types and overage on cost per square foot.
- Switch type to match each floor
- Compare 5–20% overage side by side
- Save the PDF material list for the quote
7 tips for the right underlayment order
Small habits keep your count right and your floor quiet, flat, and moisture-safe for the long haul.
Underlayment calculator FAQ
The counts, coverage rates, and U.S. cost questions people ask most before ordering underlayment.
Measure the length and width of the area in feet, add closets and hallways, then add a waste allowance for cuts. That total in square feet is the amount to buy.
Roll goods (foam, cork, felt, poly) are divided by the roll’s coverage, and sheet goods (plywood, cement board) by the sheet size. A 300 sq ft room with 10% waste comes to 330 sq ft — about 4 foam rolls at 100 sq ft each, or 11 plywood panels.
Match the underlayment to both the finished floor and the subfloor. Foam or cork goes under floating laminate and luxury vinyl plank; felt or rosin paper is a slip sheet under nail-down solid hardwood.
A 6-mil poly vapor barrier goes over concrete slabs, plywood or OSB panels smooth out a rough subfloor, and cement backer board is the rigid base under tile.
Most floating laminate needs a thin foam underlayment for cushion and sound. Many rigid-core vinyl planks, though, already have an attached pad — adding a separate one under those can make the floor too soft and may void the warranty.
Check the plank’s spec first: if it has no attached pad, add a compatible foam or cork underlayment; if it does, skip it.
Yes, over a concrete slab a 6-mil polyethylene vapor barrier stops slab moisture from reaching the floor above. Overlap the seams by 6 to 8 inches and tape them, which is why a vapor-barrier order includes a bit more waste.
Some floating-floor underlayments have a moisture barrier built in — don’t stack two. Always follow the flooring manufacturer’s moisture guidance.
It depends on the product. Foam and cork rolls commonly cover about 100 sq ft, felt and rosin paper come in large rolls around 500 sq ft, and 6-mil poly vapor barrier often runs about 1,000 sq ft.
Coverage varies a lot by brand and thickness, so always read the roll label and set that number in the calculator before ordering.
Divide your buy area by the sheet size and round up: 3 by 5 boards cover 15 sq ft each, and 4 by 8 boards cover 32 sq ft. A 300 sq ft room with 10% waste comes to 330 sq ft, which is about 22 of the 3 by 5 boards.
Backer board also needs thinset spread underneath it, corrosion-resistant screws on roughly an 8-inch grid, and alkali-resistant tape over the seams.
Allow about 10% for most underlayments in a simple rectangular room, and around 15% for a vapor barrier because the seams overlap, or for cut-heavy rooms with lots of angles and closets.
Keep the offcuts — they’re handy for patching, and buying a little extra beats coming up short mid-install.
No. Different floors need different underlayments — foam for floating floors, felt for nail-down wood, cement board for tile, poly over concrete — and they aren’t interchangeable.
You also shouldn’t stack pads: doubling up foam makes a floating floor too soft, can cause the locking joints to fail, and often voids the warranty. Use one correct layer for the job.
General Estimating Notice: This calculator sizes rolls, sheets, fasteners, bond materials, and cost from your area, product coverage, and the prices you enter, using typical 2024–2025 U.S. figures. Actual quantities and costs vary with underlayment type, roll or sheet size, subfloor condition, layout, region, and installer. Coverage differs by brand and thickness, so always confirm the label, match the underlayment to your finished floor and subfloor, and follow the manufacturer’s instructions for moisture barriers and installation. For planning purposes only.