Carpet is measured and sold by the square yard, and the starting math is simple: room area divided by 9. The catch is the roll – carpet comes in fixed widths, most commonly 12 feet, so wide rooms need seams and extra material. Here is the formula, a chart, and worked examples.
The quick answer
Square yards of carpet = room length x width ÷ 9. A 12 x 12 room (144 sq ft) needs 16 square yards as the area-based minimum. For cuts, doorways and pile direction, a 10 percent example allowance works like this: multiply the square feet by 1.10 first, then divide by 9. Rooms wider than the 12 foot roll need a seam, and the cut plan – not bare area – decides what you actually buy.
The formula
Area (sq ft) = length x width. Square yards = area ÷ 9. With an allowance, apply it before dividing: square yards = area x 1.10 ÷ 9. Convert back to square feet by multiplying yards by 9 if the carpet is priced per square foot.
Square yards by room size
Area-based minimum counts divide the area by 9; the allowance column multiplies by 1.10 first. The 10 percent is an example, not a universal waste rate, and neither column accounts for seams in rooms wider than the roll.
| Room size | Area (sq ft) | Square yards (area minimum) | Square yards (with 10%) |
|---|---|---|---|
| 10 x 10 | 100 | 11.1 | 12.2 |
| 10 x 12 | 120 | 13.3 | 14.7 |
| 12 x 12 | 144 | 16.0 | 17.6 |
| 12 x 15 | 180 | 20.0 | 22.0 |
| 12 x 18 | 216 | 24.0 | 26.4 |
| 15 x 15 | 225 | 25.0 | 27.5 |
| 15 x 20 | 300 | 33.3 | 36.7 |
| 20 x 20 | 400 | 44.4 | 48.9 |
Worked examples
12 x 12 bedroom
Area: 144 sq ft ÷ 9 = 16 square yards as the area-based minimum. A 12 foot roll covers this room in one width, so no seam. With the 10 percent example allowance: 144 x 1.10 = 158.4 sq ft, and 158.4 ÷ 9 = 17.6 square yards – in practice, a cut about 12 ft x 13 ft 3 in from the roll.
14 x 16 living room
Area: 224 sq ft ÷ 9 = 24.9 square yards by area alone – but the 14 ft width is wider than the standard 12 ft roll, so this room needs a second strip and a seam. What you buy depends on the cut layout the installer plans, and it will be more than the area minimum. This is the room where a professional measure pays for itself.
Tips before you buy
- Measure at the widest points, including doorways, closets and alcoves – carpet runs into them.
- Rolls are fixed widths: 12 feet is the most common, with 13 ft 6 in and 15 ft options for some styles. Any room wider than the roll needs a seam and extra material.
- Pile direction matters: every piece in a room must run the same way, or the carpet looks like two different shades. Patterned carpet also needs extra length to match the repeat.
- The 10 percent figure is an example allowance, not a universal waste rate – seams, patterns and odd shapes push it up.
- Padding and stairs are separate: cushion is its own purchase, and stairs get measured step by step.
- Treat your number as a budget figure: retailers and installers do a final professional measure before cutting, and their cut plan rules the order.
Sources
- Home Depot: how to install carpet – measuring the room and the square-yard convention
- Carpet Captain: carpet roll sizes – the 12 ft, 13 ft 6 in and 15 ft roll widths
- Colorado Carpet: seam placement – why rooms wider than the roll need a seam
Related calculators and guides
- Square footage calculator – measure the room first
- How many boxes of laminate flooring do I need
- How many tiles do I need for a floor
- How much baseboard do I need – the trim that finishes the edges
Estimates only. This is general guidance, not professional advice. Confirm details with your supplier, installer or local building department.