Underlayment Roll Count Calculator

Net area is typed area plus length times width. Overlap is a dimensionless percent. Roll coverage select libraries are system-aware (US ~100 sq ft class vs Metric ~10 m2 class) with values stored in sq ft. Related leaves: flooring boxes and subfloor sheets. Attached-pad LVP may need zero separate rolls – read the flooring instructions.

How do you calculate underlayment with overlap?

Measure the rectangle or type a known area. Enter roll coverage from the package. Choose an overlap percent (this tool defaults to 5%). Order area equals net area times (1 + overlap/100). Rolls equal ceil(order area / roll coverage). The FormulaCallout matches the 168 sq ft / 100 sf roll / 5% golden case.

Why does underlayment need an overlap percent?

Rolls rarely land on exact room dimensions. Seams, door cutouts, and wall returns consume a little coverage beyond the flat rectangle. A 5% overlap is a light planning allowance; 10% is safer when the room has many closets or when the manufacturer wants generous side laps. This percent is not a moisture design factor – vapor retarder rules come from the flooring system instructions.

Foam vs cork vs felt – does the formula change?

Quantity math is the same for foam, cork, felt, and thin polyethylene sheet: order area divided by roll coverage, rounded up. What changes is acoustic rating, thickness, and whether the finished flooring allows the product. Always pair underlayment SKUs with the flooring warranty requirements.