Carpet

Carpet roll math: why a 13 ft room costs so much more than a 12 ft one

Carpet is bought by the length of a roll 12 ft wide. A room up to 12 ft wide in one direction takes one piece. A room an inch wider takes two, and pays for a whole second strip.

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The roll decides the order

Broadloom carpet is made in rolls of fixed width, 12 ft in the US, with 13.5 ft and 15 ft available for some products. The installer cuts lengths from the roll, called strips or drops, and lays them side by side. You pay for every strip in full, including the part that is trimmed off at the walls. So the quantity of carpet depends not on the area of the room but on how many strips it takes and how long they are.

strips = room dimension across the roll ÷ roll width, rounded up strip length = room dimension along the roll + 6 in of trim carpet = strips × strip length × roll width square yards = carpet in sq ft ÷ 9

A room that fits

A 15 × 12 ft bedroom

  • Run the roll along the 15 ft length: the 12 ft width is covered by one strip
  • Strip: 15 ft + 0.5 ft trim = 15.5 ft of roll
  • Carpet: 15.5 × 12 = 186 sq ft = 20.7 sq yd for a 20 sq yd room

Run the other way, the room would need 2 strips of 12.5 ft, 25 ft of roll, 33.3 sq yd and a seam. The direction alone is a 60% difference.

A room that does not

A 14 × 13 ft bedroom

  • Both dimensions exceed 12 ft, so either way takes 2 strips
  • Best: 2 strips of 13.5 ft = 27 ft of roll, 324 sq ft, 36 sq yd, 1 seam
  • The room is 182 sq ft, 20.2 sq yd; the second strip is 12 ft wide but only 1 ft of it is needed
  • At $32 per sq yd: $1,152

On a 13.5 ft roll the same room takes one piece 14.5 ft long, 21.8 sq yd; on a 15 ft roll, 13.5 ft long, 22.5 sq yd. If the carpet you want comes in a wider roll, it can save a third of the cost in a room like this.

The carpet calculator lays the roll both ways for any room and picks the layout with fewer seams and less carpet.

The offcut is not always waste

In the 14 × 13 ft room, most of the second strip is offcut: a piece about 11 ft wide and 13.5 ft long. That is enough to carpet a closet, a hallway or a small second room in the same carpet. When you carpet several rooms, give the installer or store the dimensions of all of them; a good estimator plans the cuts together and the total can be much less than the rooms counted one by one. Seams in fill pieces are normal in closets.

Pile direction

Carpet pile leans one way, and it looks lighter or darker depending on which way you look at it. Every piece in a room must have its pile running the same direction, or the two sides of a seam look like different colours. That rules out turning a fill piece sideways to save carpet, and it is why a carpet order is sometimes larger than a puzzle-solving approach suggests. Usually the pile runs toward the main door or away from the main window.

Where the seams go

Seams are least visible when they run toward the main source of light rather than across it, are kept out of doorways and traffic lanes, and are not within a couple of feet of a wall. Sometimes the layout that puts the seam in the best place costs more carpet. The carpet seam planner compares the layouts: in an 18 × 14 ft room, strips across the room use 29 ft of roll and strips along the long walls use 37 ft, the same single seam, but in a different place.

Pattern repeat

A patterned carpet must match at the seams, so each strip after the first may need up to one extra pattern repeat of length. With a large repeat, that adds several feet per strip. Plain and textured carpets have no repeat.

Checking a quote

Carpet quotes are usually in square yards. Check that the yardage is what the strips require, not the room’s area: a quote for 20.2 sq yd for the 14 × 13 ft room is impossible from a 12 ft roll, and a store that delivers 36 sq yd after quoting 20 has simply quoted wrong. Check too whether pad, installation, tack strip, removal of the old carpet, moving furniture and transitions are included or extra. The units guide explains square yards.

Under and around the carpet

Every room also needs pad, cut to the room rather than the strips, and tack strip around the walls. The carpet padding calculator and the tack strip calculator count them, and the carpet padding guide explains density and thickness. For stairs, the stair carpet guide covers the different arithmetic of treads and risers.

Carpet tiles avoid the problem

Carpet tiles, usually 24 inches or 50 cm square, are counted by area like boxed flooring, with 3% to 10% waste depending on the pattern. They have no roll width and no seam problem, and a stained tile can be replaced. The carpet tiles calculator counts them.

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