Flooring: Underlayment Rolls Needed

All versions

Underlayment ships in rolls that each cover a fixed area. Divide the room square footage by the roll's coverage and round up — a half-used roll still had to be bought whole.

Quick formula: Area over roll coverage, rounded up:

=ROUNDUP(B2/C2,0)

240 square feet of floor with 100-square-foot rolls needs 3 rolls — two and a bit, rounded up.

Functions used (tap for the full reference guide):

ROUNDUP

The example

Three areas with different roll sizes — the whole-floor job uses a bigger 200-square-foot roll.

	A	B	C	D
1	Area	Sq ft	Roll (sqft)	Rolls
2	Living room	240	100	3
3	Bedroom	180	100	2
4	Whole floor	850	200	5

The formula

ROUNDUP converts the fractional roll count into whole rolls to order:

=ROUNDUP(B2/C2,0) // floor area over roll coverage, rounded up

How it works

One division, always up:

B2/C2 divides the floor area by the area one roll covers — 240 over 100 is 2.4.
ROUNDUP(...,0) makes that 3, because you cannot buy 0.4 of a roll.
Keep the roll coverage in a cell — foam, felt, and cork rolls all cover different areas.

Underlayment overlaps or butts with tape at the seams, which eats a little coverage. If your rolls run tight, drop the coverage figure a few percent rather than trusting the label area.

Try it: interactive demo

Interactive

Enter the floor area and the coverage of one roll.

Floor area (sq ft)

Roll coverage (sq ft)

Variations

Add a seam-overlap allowance

Trim the effective coverage for the lap at each seam.

=ROUNDUP(B2/(C2*0.95),0)

Rolls plus seam tape

One roll of tape per few rolls of underlayment is a common pairing.

=ROUNDUP(ROUNDUP(B2/C2,0)/3,0)

Pitfalls & errors

Do not round rolls down. A floor that needs 2.4 rolls and gets 2 leaves a bare strip, and the next roll may be a different lot with a slightly different thickness.

Some click-lock floors have the pad pre-attached and need no separate underlayment. Check the plank before ordering rolls you will not use.

Practice workbook

📊

Download the free Flooring: Underlayment Rolls Needed practice workbook

Edit the yellow area and roll-coverage cells; the roll count recalculates.

Frequently asked questions

How much does one roll cover?

It varies by product — standard foam rolls often cover 100 square feet, premium and cork rolls sometimes 200 or more. The label states it; put that number in the coverage column.

Do I need underlayment over concrete?

Usually a moisture-barrier underlayment is required over a slab, and it may cover less area per roll than a basic foam. Use the product's own coverage figure for the slab rooms.

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Function references: ROUNDUP