Answer first
What this calculator tells you
Estimate square yards and roll length of carpet needed for a room. Price carpet by the square yard and check the roll length before you order. Formula: Area to buy = room length × width × (1 + waste); square yards = area ÷ 9; roll length (ft) = area to buy ÷ roll width. At the worked-example inputs, the square yards to buy is 22. Holding every other input steady, moving room length (ft) from 12 to 18 moves the result from 17.6 to 26.4.
Transparent method
The formula
Price carpet by the square yard and check the roll length before you order.
Worked example
Example inputs
How to interpret the result
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.
At the worked-example inputs the square yards to buy is 22. It rises with room length (ft), room width (ft) and waste allowance.
These are material-quantity estimates. Always add a waste and overage margin, and confirm actual coverage with your specific product and supplier before purchasing.
Before you rely on it
What to check
Sketch the seams and the direction of the pile. Carpet must run one way, and a bad seam layout can waste a full width.
The common error
Where people go wrong with carpet calculator
Buying square yards without checking the roll. A room a foot wider than the roll can double the length you have to buy.
Sensitivity evidence
How room length (ft) changes the square yards to buy
Holding every other input at the worked-example value, moving room length (ft) from 12 to 18 moves the square yards to buy from 17.6 to 26.4: a spread of 8.8, or 40% of the worked-example result.
| Room length (ft) | Square yards to buy | Roll length needed (ft) |
|---|---|---|
| 12 | 17.6 | 13.2 |
| 14 | 20.5 | 15.4 |
| 15worked example | 22 | 16.5 |
| 17 | 24.9 | 18.7 |
| 18 | 26.4 | 19.8 |
Every input, tested
Which input moves the square yards to buy most
Of the 3 inputs, room length (ft) moves the square yards to buy most (4.4 across the range tested) and waste allowance moves it least (0.8).
| Input | Tested from | To | Square yards to buy at each end | Swing |
|---|---|---|---|---|
| Room length (ft) | 14 | 17 | 20.5 to 24.9 | 4.4 (20%) |
| Room width (ft) | 11 | 13 | 20.2 to 23.8 | 3.7 (17%) |
| Waste allowance | 8.0% | 12.0% | 21.6 to 22.4 | 0.8 (3.6%) |
Two variables at once
Square yards to buy by room length (ft) and room width (ft)
Across the grid the square yards to buy runs from 14.7 to 30.8. Moving room length (ft) from 12 to 18 shifts it by 8.8 at the middle column, and moving room width (ft) from 10 to 14 shifts it by 7.3 at the middle row, so room length (ft) is the bigger lever here.
| Room length (ft) \ Room width (ft) | 10 | 12 | 14 |
|---|---|---|---|
| 12 | 14.7 | 17.6 | 20.5 |
| 14 | 17.1 | 20.5 | 24 |
| 15 | 18.3 | 22 | 25.7 |
| 17 | 20.8 | 24.9 | 29.1 |
| 18 | 22 | 26.4 | 30.8 |
The highlighted cell is the worked example: 22.
Step by step
The worked example, input by input
| Input | Value used | What it means |
|---|---|---|
| Room length (ft) | 15 | Enter the room length (ft) used in this calculation. |
| Room width (ft) | 12 | Enter the room width (ft) used in this calculation. |
| Carpet roll width (ft) | 12 ft roll | Carpet is sold in rolls 12 or 15 feet wide. |
| Waste allowance | 10.0% | Seams, pattern match and trimming. |
| Square yards to buy | 22 | |
| Roll length needed (ft) | 16.5 | |
Inputs, definitions and assumptions
Room length (ft)
Enter the room length (ft) used in this calculation. The prefilled worked-example value is 15.
Room width (ft)
Enter the room width (ft) used in this calculation. The prefilled worked-example value is 12.
Carpet roll width (ft)
Carpet is sold in rolls 12 or 15 feet wide. The prefilled worked-example value is 12 ft roll.
Waste allowance
Seams, pattern match and trimming. The prefilled worked-example value is 10.0%.
How to use this calculator
- 1Verify the inputs. Gather room length (ft), room width (ft), carpet roll width (ft) and waste allowance from your own documents; the prefilled values are examples.
- 2Save a baseline. The worked example puts the square yards to buy at 22. Store your own version of it as Scenario A.
- 3Test one change. Start with room length (ft), the input with the biggest effect here: moving room length (ft) from 14 to 17 takes the square yards to buy from 20.5 to 24.9, a swing of 20% of the worked-example figure.
- 4Check the extremes. At half the example room length (ft) (7.5) the square yards to buy is 11; at double (30) it is 44.
People also ask
Frequently asked questions
How do you calculate carpet?
Area to buy = room length × width × (1 + waste); square yards = area ÷ 9; roll length (ft) = area to buy ÷ roll width. Enter waste allowance in percent (10 means 10%). At the worked-example inputs the square yards to buy is 22.
What does the carpet result mean?
Price carpet by the square yard and check the roll length before you order. At the worked-example inputs the square yards to buy is 22. It rises with room length (ft), room width (ft) and waste allowance.
How much does room length (ft) change the square yards to buy?
Holding every other input at the worked-example value, moving room length (ft) from 12 to 18 moves the square yards to buy from 17.6 to 26.4, a spread of 8.8.
What are the limits of this carpet calculator?
These are material-quantity estimates. Always add a waste and overage margin, and confirm actual coverage with your specific product and supplier before purchasing. The tables on this page test room length (ft) only from 12 to 18; a value outside that range is not tabulated here.
Which input moves the square yards to buy most in the carpet calculator?
Ranked by how far each moves the square yards to buy across the range tested: room length (ft) (4.4, 20%), room width (ft) (3.7, 17%) and waste allowance (0.8, 3.6%).
If I double room length (ft) in the carpet calculator, does the square yards to buy double?
Doubling it from 15 to 30 takes the square yards to buy from 22 to 44, which is 2.00 times the worked-example figure. So the result scales almost exactly in proportion. Halving it to 7.5 gives 11.
How much does room width (ft) matter in the carpet calculator?
The worked example uses 12. Holding every other input at its worked-example value, moving room width (ft) from 11 to 13 takes the square yards to buy from 20.2 to 23.8, a swing of 17% of the worked-example figure.
How much does waste allowance matter in the carpet calculator?
The worked example uses 10.0%. Holding every other input at its worked-example value, moving waste allowance from 8.0% to 12.0% takes the square yards to buy from 21.6 to 22.4, a swing of 3.6% of the worked-example figure.
Which inputs change the roll length needed (ft) in the carpet calculator?
At the worked-example inputs it is 16.5. Room length (ft) takes it from 15.4 to 18.7, room width (ft) takes it from 15.1 to 17.9 and waste allowance takes it from 16.2 to 16.8.
Why does a sheet-goods cut list still need a waste allowance beyond the raw area?
Saw kerf removes a small sliver of material with every cut, and real pieces rarely nest perfectly against a sheet's edges the way a pure area calculation assumes. A 10 to 15% allowance on top of the exact geometric area covers both without forcing a mid-project supply run.
Sources and evidence
Free Calculators Online is independent and is not affiliated with or endorsed by the source organizations. Educational estimates only.