How much carpet for a 12x12 room?

The offcut is bigger than the floor

A 12 × 12 room is 144 sq ft. On the 12 ft roll that virtually all residential carpet comes on, you buy 300 sq ft — and throw away 156. The bin gets more carpet than the bedroom does.

That is not a rounding artefact, it is the geometry of a room that sits a whisker over the roll on both sides once the installation standard's trim is added. Each span becomes 12 ft 6 in, each needs two drops, and the second drop of each pair is almost entirely offcut. You are paying 2.08 times the floor area.

A square room is the one case with nothing to decide

Every other room this calculator handles has two answers, because you can run the strips along the length or along the width and one of them is cheaper. A square room has one. Both orientations here give exactly 300 sq ft — identical, because there is no long side to exploit.

So the usual advice, turn the layout round and compare, is worth nothing on a 12 × 12. Every other lever still works, and one of them is unusually powerful.

Six inches decides whether you pay 300 or 144

Almost no room called "12 by 12" measures 12 ft 0 in square. Measure it properly before ordering, because the boundary runs right through the nominal size:

Actual room	Carpet to buy	Seams
12 ft 0 in square	300 sq ft	1
11 ft 6 in square	144 sq ft	0

Half a foot in each direction, and the order halves. An 11 ft 6 in room plus 3 in of trim at each wall is 12 ft 0 in exactly — one drop, no seam, no second strip to pay for. If your room measures anywhere under 11 ft 6 in, say so when you order; if it is 12 ft 1 in, there is nothing to be done about it.

The one question worth asking a supplier

If a wider roll were available, this is the room where it would pay for itself rather than merely removing a seam: 12 ft 6 in of span clears a 13.5 ft width in a single drop, taking the order to 168.75 sq ft — 44% less carpet than the 12 ft roll, with no seam at all.

Two honest caveats before you count on that. Every roll we could actually verify was 12 ft — Shaw's entire residential listing and its commercial broadloom, checked in July 2026. And the 13.5 ft width itself comes from a single Carpet and Rug Institute page rather than from any product we could find; four routes failed to turn up a wider roll for sale. That is a record of where we looked, not proof the width is unavailable. So it is worth one question to a supplier, and worth nothing at all until they answer it.

If you are stuck with 300 sq ft, place the seam deliberately

One seam is unavoidable on a 12 ft roll here. CRI 105 asks for seams to run the length of the room, to have main traffic running parallel to them rather than across, and never to sit perpendicular to a doorway — so decide which wall the narrow strip goes against before anything is cut, and keep it away from the door and out of the light from the window.

Sources: CRI 105, Standard for Installation of Residential Carpet (2019), section 5.3 for the 3 in trim allowance and 5.1 for seam placement, and The Carpet and Rug Institute, Finding the Right Carpet for the 12, 13.5 and 15 ft broadloom widths.