Carpet calculator

Q: How wide is a roll of carpet?

**12 ft**, on everything we could actually check: all 136 carpets in Shaw's residential listing in July 2026, and Shaw Contract's commercial broadloom. CRI describes continuous dyeing as running "12-foot-wide carpets, sewn end to end" for the residential market. CRI also lists **13.5 and 15 ft** widths, but that sentence is the only source we found for them — we could not confirm either on a manufacturer or retailer product page, so measure your roll rather than assuming a wider one is available.

Q: How many square yards is my room?

Divide square feet by **9**, not by 3 — the commonest mistake in carpet pricing, and it triples the answer. A 20 × 13 ft room is 260 sq ft, or 28.9 sq yd of floor; the carpet you actually buy for it on a 12 ft roll is 324 sq ft, **36 sq yd**. Always compare quotes in the same unit, because some yards still price per square yard and some per square foot.

Enter the room and the width of the roll you are buying. Carpet is cut off a roll of fixed width, so the answer depends on which way the strips run — and on the 3 in of trim the installation standard requires at every wall.

Room length The longer wall. Measure into doorways and closets you are carpeting, and take the widest point if the walls are not parallel. Room width Roll width Measure your own roll and use that. 12 ft is what we actually found in stock; the Carpet and Rug Institute also lists 13.5 and 15 ft, but we could not confirm either on a manufacturer or retailer product page, so treat them as something to ask about. Trim allowance at each wall CRI 105 requires at least 3 in along each wall. It is added to both ends of every strip, so it adds 6 in to each room dimension — which is why a 12 ft room will not fit a 12 ft roll.

Carpet to buy 324 sq ft

In square yards 36 sq yd Carpet is still quoted per square yard in many places. One square yard is 9 square feet, not 3.

Length off the roll 27 linear ft What actually gets cut. You buy a length of the full roll width, so this is the number to give the store.

Seams 1 seams Strips minus one. CRI 105 says to keep seams to a minimum and never run them perpendicular to a doorway.

Offcut you pay for 64 sq ft Carpet bought minus floor covered. The roll width is fixed, so part of the last strip is usually waste.

If the strips ran the other way 492 sq ft The same room with the drops turned 90°. The gap between this and the figure above is what choosing the direction is worth.

Carpet is not sold by the area

It is cut off a roll, and the roll has a fixed width. Every strip comes off at that full width whether the room needs all of it or not, so the question is never "how many square feet is the floor" — it is how many strips fit, and which way they run.

That gives two candidate layouts for any rectangular room: strips laid across the length, or strips laid across the width. Choosing the cheaper one is often worth a third of the order. A 20 × 13 ft room on a 12 ft roll takes 324 sq ft one way round and 492 sq ft the other — the same floor, the same carpet, 168 sq ft apart.

The three inches that decide the seam

CRI 105, the residential installation standard, requires carpet to be cut "allowing at least 3 inches along each wall for trimming". Walls are not straight and rooms are not square; the fitter needs that margin to scribe to.

Three inches at each wall adds six inches to each room dimension, and that one detail decides whether a room fits a roll at all:

A 20 × 12 ft room, ignoring trim, is a perfect fit — 12 ft of room on a 12 ft roll, 240 sq ft, no seam.
The same room done to the standard needs 12.5 ft across, which is two drops: 300 sq ft and one seam.

A 25% jump, from an input an area-only estimate never sees. The cliff is sharp, too: at 20 × 11 ft 6 in you buy 246 sq ft with no seam, and at 20 × 11 ft 8 in you buy 292 sq ft with a seam. Two inches of room, 46 sq ft of carpet.

The width is 12 ft, and a wider one would not automatically be cheaper

Every one of the 136 carpets in Shaw's residential listing was 12 ft when we checked in July 2026, and Shaw Contract's commercial broadloom is 12 ft too. Plan on 12 ft unless you have been told otherwise.

The Carpet and Rug Institute also lists 13.5 and 15 ft. That single sentence is the only source we found: four routes turned up no wider roll we could point at, and Home Depot's own filter offers 12, 13 and 13.2 ft — the last being the 4 m metric width, which CRI does not mention. That is not evidence the wider rolls do not exist, only a record of where we looked. If you are quoted one, measure it and enter it.

Worth knowing anyway, because the instinct is wrong. Our 20 × 13 ft room, trimmed to the standard:

Roll width	Carpet to buy	Seams
12 ft	324 sq ft	1
13.5 ft	276.8 sq ft	0
15 ft	307.5 sq ft	0

The widest roll loses. 13 ft of room plus 6 in of trim is exactly 13.5 ft, so nothing is wasted across the width, while 15 ft clears the room and bills you for the 1.5 ft you did not use. The best width lands just above your room dimension plus the trim — not at the biggest number available.

What this assumes about how carpet is sold, and what we could not check

The arithmetic above assumes you can buy any length off the roll. That much holds up: Home Depot runs "Cut to Length" and "Carpet by the Foot" as its own ordering categories. What we could not confirm is whether a minimum length applies — the retailer ordering terms we would need are behind pages that refuse automated access, so treat a very small order as a question for the seller rather than something this page has verified.

The bigger caveat is that the cheaper orientation is not always the one you are allowed to use. The seam rules below are constraints, not preferences, and CRI's model specification has the vendor supply "shop drawings of areas to be carpeted showing seams and cut sheet for carpet" — the layout is agreed between you, the dealer and the fitter. Take the cheaper figure as the opening position in that conversation, not as the answer. If the only layout that keeps a seam out of the doorway is the expensive one, the expensive one is correct.

Two more things sit outside this calculation entirely: stairs, and any room that is not a rectangle. Both need their own measure.

Where the seam goes

CRI 105 is specific, and the rules cost nothing to follow if you decide before cutting. Seams should run the length of the room; main traffic should run parallel to a seam rather than across it; seams should not sit where daylight rakes across them, should stay clear of pivoting traffic, and should never be perpendicular to a doorway.

The standard also requires that adjacent pieces of the same carpet have the same pile direction. Pile lay is why carpet looks lighter from one end of a room than the other, and two strips laid head-to-toe read as two different colours under the same light. It is not a defect and it cannot be fixed after the fact.

Stairs are a separate calculation. Each step needs tread plus riser plus the nosing wrap in one continuous piece, and CRI 105 asks for the nose to be rounded 3/4 to 1 in — measure the stair run and add it as its own order rather than hoping the room offcut covers it.

Common cases

How much carpet for a 12x12 room?

Questions people ask

How wide is a roll of carpet?

12 ft, on everything we could actually check: all 136 carpets in Shaw's residential listing in July 2026, and Shaw Contract's commercial broadloom. CRI describes continuous dyeing as running "12-foot-wide carpets, sewn end to end" for the residential market. CRI also lists 13.5 and 15 ft widths, but that sentence is the only source we found for them — we could not confirm either on a manufacturer or retailer product page, so measure your roll rather than assuming a wider one is available.

Why does a 12 ft wide room not fit a 12 ft roll?

Because of trim. CRI 105 requires cutting the carpet "allowing at least 3 inches along each wall", which adds 6 in across the room — so a 12 ft room needs 12.5 ft of carpet and that is two strips. A 20 × 12 ft room goes from 240 sq ft and no seam on paper to 300 sq ft and one seam in reality. Rooms just under the roll width are the ones to measure carefully.

Does it matter which way the carpet runs?

Often more than anything else you decide. A 20 × 13 ft room on a 12 ft roll needs 324 sq ft with the strips one way and 492 sq ft with them the other. Run the calculator and compare the two figures before you order. The catch is that direction is also a seam-placement and pile-direction decision, so the cheaper layout is not automatically the right one.

Is a wider roll always less carpet?

No. Wider rolls mean fewer seams, not less material. For a 20 × 13 ft room a 13.5 ft roll needs 276.8 sq ft while a 15 ft roll needs 307.5 sq ft, because 13 ft of room plus the trim allowance uses a 13.5 ft width exactly and wastes 1.5 ft of a 15 ft one. The best width is the one closest above your room dimension plus 6 in. Note that both of those widths come from CRI's list rather than from a roll we could find for sale — the principle holds whatever widths you are offered.

How many square yards is my room?

Divide square feet by 9, not by 3 — the commonest mistake in carpet pricing, and it triples the answer. A 20 × 13 ft room is 260 sq ft, or 28.9 sq yd of floor; the carpet you actually buy for it on a 12 ft roll is 324 sq ft, 36 sq yd. Always compare quotes in the same unit, because some yards still price per square yard and some per square foot.

Last reviewed 2026-07-31