How the carpet calculation works
Broadloom carpet is made in rolls of a set width, most often 12 ft in the US. Each piece you cut is the full roll width, so a room narrower than the roll still uses a full-width piece, and a wider room needs a second strip and a seam.
- Strips. Divide the room width by the roll width and round up.
- Length off the roll. Multiply the strips by the room length, then add your trimming allowance.
- Carpet to buy. Multiply that length by the roll width. Divide square feet by 9 for square yards.
- Direction. The calculator tries the strips both ways and shows the one that uses less carpet.
sq yd = strips × room length × (1 + extra) × roll width ÷ 9
Worked example
A 15 × 12 ft bedroom has 180 sq ft of floor, which is 20 sq yd. A 12 ft roll covers the width in one strip. Add 10 percent to the 15 ft length and you need 16.5 ft off the roll. That is 198 sq ft, or 22 sq yd, with no seams. In metric, the room is 16.7 m² and you buy 5.03 m off a 3.66 m roll, 18.4 m².
An 18 × 14 ft living room is different. Its floor is 252 sq ft (28 sq yd), but neither side fits a 12 ft roll. Two strips laid across the 14 ft width need 30.8 ft of carpet: 370 sq ft, or 41.1 sq yd, with one seam. A 15 ft roll covers the room in one strip of 19.8 ft, just 33 sq yd. The roll width can matter more than the room size.
Common roll widths
| Roll width | Metric | Where you see it |
|---|---|---|
| 12 ft | 3.66 m | The usual US and Canadian width |
| 15 ft | 4.57 m | Some US styles, handy for wider rooms |
| 13 ft 2 in | 4 m | Common in Australia, the UK and Europe |
Ask the store which widths the carpet you like is made in before you plan the layout.
Seams and pile direction
- Every piece in a room must have its pile running the same way, or the pieces look like different colors. That is why you cannot always rotate offcuts to fill gaps.
- Installers try to keep seams out of doorways and main walkways, and often run them toward the main window so light does not cross them.
- Patterned carpet must line up at seams. Add the pattern repeat to each strip, which can mean much more than 10 percent extra.
Pad, stairs and closets
Carpet pad is not directional, so you can piece it together: buy about the floor area. Measure closets with the room they open off, and run the carpet to the middle of the door where it meets another floor. Stairs are measured step by step and are best left to the installer, who will plan the pile direction down the flight.
Comparing quotes
Carpet is priced per square yard in some stores and per square foot in others. Divide a price per square yard by 9 to compare it with a price per square foot. Ask whether the quote is for the floor area or for the carpet cut off the roll, because the second is what you pay for. Check what is included: pad, installation, removing and disposing of the old carpet, moving furniture, stairs, and transition strips are often itemized separately.
Before you order
Most retailers send someone to measure, and that measurement sets the price. Use this calculator to sense-check the quote and compare roll widths. For the room's floor area alone, the square footage calculator is quicker. Moving heavy furniture and carpet rolls is a two-person job; lift with your legs.
Frequently asked questions
How many square yards of carpet do I need for a 12 × 15 room?
The floor is 20 sq yd. With a 12 ft roll and 10 percent for trimming you buy 16.5 ft off the roll, which is 22 sq yd.
What width does carpet come in?
Most carpet in the US and Canada comes in 12 ft rolls, with some styles in 15 ft. In Australia, the UK and Europe, 4 m is common.
How do I convert square feet to square yards?
Divide by 9. A 180 sq ft room is 20 sq yd.
How much carpet pad do I need?
About the floor area, because pad can be pieced together without matching. A 15 × 12 ft room needs about 20 sq yd of pad.