Enter the rectangular room length and width, roll width and an extra length percentage. Carpet strips run along the entered room length. The calculation rounds the number of full-width strips up, then adds the length allowance.
Swap room length and width to compare seam orientation; nap or pattern direction may rule out that rotation.
This is a full-length strip layout, without reusing offcuts across another room. Pattern repeats, seams, joins, closets and stairs need an installer’s cutting plan. The extra percentage is an entered assumption, not a guarantee of enough matching material.
Padding and installation are separate.
Carpet: worked example
| Room length (ft) | 15 |
|---|---|
| Room width (ft) | 12 |
| Carpet roll width (ft) | 12 ft roll |
| Waste allowance | 10.0% |
| Square yards to buy | 22 |
| Roll length needed (ft) | 16.5 |
Common error: Buying square yards without checking the roll. A room a foot wider than the roll can double the length you have to buy.
Carpet: formula
NIST Handbook 44: Units and Systems of Measurement · Rectangle: Wolfram MathWorld
Carpet: changing Room length (ft)
| Room length (ft) | Square yards to buy | Roll length needed (ft) |
|---|---|---|
| 12 | 17.6 | 13.2 |
| 14 | 20.5 | 15.4 |
| 15 (example) | 22 | 16.5 |
| 17 | 24.9 | 18.7 |
| 18 | 26.4 | 19.8 |
Carpet: compare input ranges
| Input | Tested from | To | Square yards to buy: low input | Square yards to buy: high input | Swing |
|---|---|---|---|---|---|
| Room width (ft) | 11 | 13 | 22 | 44 | 22 (100%) |
| Carpet roll width (ft) | 12 ft roll | 15 ft roll | 22 | 27.5 | 5.5 (25%) |
| Room length (ft) | 14 | 17 | 20.5 | 24.9 | 4.4 (20%) |
| Waste allowance | 8.0% | 12.0% | 21.6 | 22.4 | 0.8 (3.6%) |
Carpet: individual input comparisons
| Input | Value | Square yards to buy | Roll length needed (ft) |
|---|---|---|---|
| Room length (ft) | 12 | 17.6 | 13.2 |
| 14 | 20.5 | 15.4 | |
| 15 | 22 | 16.5 | |
| 17 | 24.9 | 18.7 | |
| 18 | 26.4 | 19.8 | |
| Room width (ft) | 10 | 22 | 16.5 |
| 11 | 22 | 16.5 | |
| 12 | 22 | 16.5 | |
| 13 | 44 | 33 | |
| 14 | 44 | 33 | |
| Carpet roll width (ft) | 12 ft roll | 22 | 16.5 |
| 15 ft roll | 27.5 | 16.5 | |
| Waste allowance | 6.0% | 21.2 | 15.9 |
| 8.0% | 21.6 | 16.2 | |
| 10.0% | 22 | 16.5 | |
| 12.0% | 22.4 | 16.8 | |
| 14.0% | 22.8 | 17.1 |
Carpet: combined input changes
| Room length (ft) / Room width (ft) | 10 | 12 | 14 |
|---|---|---|---|
| 12 | 17.6 | 17.6 | 35.2 |
| 14 | 20.5 | 20.5 | 41.1 |
| 15 | 22 | 22 | 44 |
| 17 | 24.9 | 24.9 | 49.9 |
| 18 | 26.4 | 26.4 | 52.8 |
Carpet: which assumptions move the result?
Carpet: values and definitions
| Quantity and definition | Value used |
|---|---|
| Room length (ft) | 15 |
| Room width (ft) | 12 |
| Carpet roll width (ft) — Carpet is sold in rolls 12 or 15 feet wide. | 12 ft roll |
| Waste allowance — Seams, pattern match and trimming. | 10.0% |
| Square yards to buy | 22 |
| Roll length needed (ft) | 16.5 |
Carpet: half and double Room width (ft)
| Room width (ft) | Square yards to buy |
|---|---|
| 6 | 22 |
| 12 | 22 |
| 24 | 44 |
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Carpet comes on wide rolls, so the length you buy depends on the roll width, not only on the room area. A 15 by 12 foot room with 10 percent waste is 198 square feet, or 22 square yards. On a 12 foot roll that is 16.5 feet of length.
The seam layout can add more, because a room wider than the roll needs a second strip.
Sketch the seams and the direction of the pile. Carpet must run one way, and a bad seam layout can waste a full width.
See the area on the square footage calculator, alternatives on the flooring and tile calculators and volume on the material pages. The paint and drywall calculators cover walls, and the unit price comparison page helps compare per-yard and per-foot prices.
Can a 13-foot-wide room fit one 12-foot-wide strip?
No. It needs a join or another orientation; area alone does not establish a workable cut.
Does the calculator choose the seam direction?
No. It uses strips parallel to the entered length. Compare the rotated dimensions only when the product’s nap and installation rules permit it.
How do I convert square feet to square yards?
Divide by 9. A 180 square foot room is 20 square yards.
Why does the roll width matter?
Carpet is cut from a fixed-width roll, so rooms that do not fit the width waste material or need seams.
Do I need padding?
Yes for most carpet. Padding adds comfort, extends carpet life and is often bought separately per square yard.