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Carpet Calculator

Use this free carpet calculator to find out how much carpet a room needs before you order. Enter the room size, pick the roll width, set the pattern repeat, and add a waste allowance. The calculator gives you the square yards, the linear feet, the number of strips, and the seams, so you can order the right amount in one trip.

How it works

Carpet is sold by the linear foot off a roll, and priced by the square yard, so this calculator works in both units. It starts with the room size and the roll width to find how many strips of carpet the room needs. A strip runs the length of the room, and its width is the roll width, so the number of strips is the room width divided by the roll width, rounded up. A room 18 feet wide on a 12-foot roll needs two strips, and the second strip is cut down to the 6 feet that are left.

The pattern repeat matters whenever the carpet has a visible design. Each strip has to start at the same point in the pattern as the one next to it, or the design will not line up across the seam. That means every strip is cut one repeat longer than the room, so a 12-inch repeat adds a foot to each strip. Plain carpet has no repeat and no extra length, which is one reason it is cheaper to install. Pick the repeat printed on the carpet sample and the calculator adds it to every strip automatically.

Waste covers the offcuts. The second strip in the example is 12 feet wide but only 6 feet of it is used, so half of that strip is waste before you even start cutting around doorways and closets. Ten percent is the default allowance, and it suits a plain rectangular room. Raise it for a patterned carpet, an L-shaped room, or a room with lots of doorways, where the cutting gets complicated. The calculator adds the waste to the linear footage, then converts to square yards by multiplying by the roll width and dividing by 9.

Seams are where two strips meet. The number of seams is always one less than the number of strips, so two strips mean one seam and three strips mean two. Seams are best placed under furniture or along the least walked part of the room, and a good installer can make them nearly invisible on plain carpet. On a patterned carpet the seam is where the pattern has to match, which is why the repeat allowance is so important. If your room is narrower than the roll width, you need one strip and there is no seam at all.

Rolls are another practical limit. A full roll is often around 100 feet long, and the calculator checks whether your order fits on one roll. If it does not, the result tells you how many rolls to order, because a second roll may come from a different dye lot and look slightly different. Measure the room at its longest and widest points, add a few inches for trimming at the walls, and measure closets and alcoves separately if they are being carpeted too.

Worked example

A bedroom measures 15 feet long by 18 feet wide. The carpet comes on a 12-foot roll, has no pattern, and the waste allowance is 10 percent.

Step 1: Find the strips — 18 ÷ 12 = 1.5, rounded up to 2 strips.
Step 2: Find the strip length — the room is 15 feet long and there is no pattern repeat, so each strip is 15 feet.
Step 3: Linear feet — 2 strips × 15 feet = 30 linear feet.
Step 4: Add waste — 30 × 1.10 = 33 linear feet to order.
Step 5: Square yards — 33 × 12 ÷ 9 = 44 square yards.
Step 6: Seams — 2 strips − 1 = 1 seam.

The room needs 33 linear feet of carpet, which is 44 square yards, with one seam down the middle. It fits easily on a single 100-foot roll, and the second strip is cut from 12 feet wide down to the 6 feet the room still needs.

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