Carpet cut from a 12 ft roll, seams and all

Carpet is roll goods. It is woven on a loom of a fixed width — 12 ft for nearly all US residential broadloom, 15 ft from a few mills, 13 ft 2 in for anything made to a four-meter loom — and it is sold by the running foot off that roll at the full width, used or not. Two consequences follow immediately and neither is visible in a square footage. The first is that any room narrower than the roll costs its own length and nothing else: an 11 ft 6 in room and a 12 ft room take exactly the same carpet off a 12 ft roll. The second is that crossing the roll width is a step change rather than a gradient. A 13 by 20 ft room needs two cuts however you turn it, but cut the long way those are two 20 ft lengths — 480 square feet of roll for 260 square feet of floor, before any trim — and cut the short way they are two 13 ft lengths, 312 square feet, for the same room. The difference is 168 square feet of carpet, bought or not bought on a decision nobody makes explicitly unless they are shown it. That is why this page prices both directions and why it never quotes a waste percentage, and it is the reason carpet has its own tool here rather than sharing the box-counting arithmetic of the flooring calculator.

The constraint that makes the layout rigid is pile direction. Every carpet leans one way down the roll, and a piece rotated to fit reflects light differently enough that it reads as a different color from across a room — not a subtle effect, and not fixable after the fact. Installers mark arrows on the back of every piece for exactly this reason. What it costs you in material is that a filler strip cannot be recovered from a crosswise offcut: it has to come off the roll at full length with its nap aligned, and the rest of that width is scrap. It also means the two cutting directions are genuinely different products rather than the same job rotated, because each puts the seam somewhere different — and a seam wants to run with the light from the main window and away from the walking line, never across a doorway. Where the leaner layout puts the seam in the wrong place, buying the dearer one is the right call, which is a judgement a calculator can inform and should not make.

Last, the units. Square yards is the trade unit and square feet is the retail one, they differ by nine, and quotes arrive in both — a $3.99 per square foot carpet is $35.91 per square yard, and a shopper comparing those two figures across two stores without checking the unit will pick the wrong one every time. Cushion is quoted the same way and is a separate order in a different width: cushion rolls are 6 ft, so a room seams the padding more often than the carpet and nobody minds, because a pad seam is taped and never seen. Carpet also has no equivalent of the spare box that a hard floor wants — there is no dye lot to match years later, only the remnant you keep rolled in the garage — which makes the offcut on this page worth actually looking at. Where the room is getting a hard surface instead, the count goes back to cartons on the flooring calculator.