Underlayment Calculator
Calculate underlayment rolls and cost for foam, cork, or felt by room size and waste factor.
Works for hardwood, laminate, and vinyl plank floor installs.
Underlayment sits between the subfloor and your finished floor. It softens the feel underfoot, reduces sound transmission (especially important in multistory homes), provides a slight thermal barrier, and in some cases acts as a vapor barrier over concrete.
The roll count is: CEIL(room area × (1 + waste%) / 100 sq ft per roll). Standard rolls are 100 sq ft (typically 3.3 ft × 30 ft). Round up to the nearest whole roll.
Choosing the type
Foam is the cheapest and most common. It compresses over time and offers minimal sound dampening compared to denser materials. Fine for laminate in a bedroom on a wood subfloor.
Cork is thicker, more resilient, and significantly better for sound absorption. Worth the extra cost in apartments or second-floor rooms where impact sound travels through the floor-ceiling assembly. Cork also provides modest thermal insulation value.
Felt (or rubber felt) is denser than foam and holds up better under heavy foot traffic and furniture. It is the better choice for high-traffic hallways or commercial-grade laminate installs.
The combination type layers foam with a built-in vapor barrier. Use this when installing over a concrete slab that might see occasional moisture: garages, basements, ground-floor slabs in humid climates. Without a vapor barrier over concrete, moisture migrates up through laminate and causes buckling.
Waste factor
10% is the right starting point for square or rectangular rooms. Add another 5% for diagonal installation (cuts are longer and generate more scrap), and another 5% for rooms with many cutouts or irregular shapes.
Underlayment is inexpensive relative to the flooring itself. Buying one extra roll costs a few dollars and avoids a second trip to the store if a cut goes wrong.
Some laminate flooring products include underlayment pre-attached to the plank. If yours does, do not add a separate foam layer. You may still need a separate vapor barrier over concrete.