Underlayment Calculator
How many rolls of flooring underlayment
Adding underlayment beneath new flooring? Enter the floor area to find how many rolls to buy.
How much underlayment?
Underlayment rolls commonly cover about 100 ft². Match the floor area (underlayment runs edge to edge with minimal overlap). Some flooring has it pre-attached — check before buying.
What underlayment does
A good underlayment cushions the floor, quiets footstep noise, smooths minor subfloor imperfections, and on concrete adds a moisture barrier that protects laminate and wood from slab humidity. Some products combine cushioning and a vapor barrier in a single roll.
Matching it to your floor
Use foam or felt underlayment under floating laminate and engineered wood; use a moisture-barrier type over concrete; and skip separate underlayment if your planks already have it pre-attached (doubling up can void the warranty). For sound control in condos, look for a high IIC/STC rating.
Underlayment Calculator: frequently asked questions
How many square feet in a roll of underlayment?
Commonly 100 ft², though some rolls cover 200 ft². Check the label.
Do I always need underlayment?
Not always — some laminate and vinyl come with it pre-attached. Add separate underlayment only if your flooring doesn't include it.
Do I need a moisture barrier under flooring on concrete?
Yes — concrete releases moisture that can damage laminate and wood. Over a slab, use an underlayment with a built-in vapor barrier (or add a separate poly sheet). Over a wood subfloor, standard foam or felt is fine.