Carpet is sold by the square yard, but it is cut from a roll that is a fixed width, so the amount you must buy is nearly always more than the floor area of the room. This carpet calculator gives you both numbers: the square yards of floor you cover, and the linear feet of roll the store has to cut for your room, including the leftover that you pay for but cannot use.
How to use the carpet calculator
- Enter the room’s length and width. For an L-shaped room, calculate each rectangle separately and add them.
- Select the roll width. 12 feet is the most common.
- Add a waste allowance for pattern matching, trimming and mistakes.
- Read the results: area, square yards to buy, roll length and the offcut.
Carpet formula
Strips = ⌈ room dimension across the roll ÷ roll width ⌉
Roll length = strips × room dimension along the roll
A square yard is 3 × 3 = 9 square feet. The calculator tries running the roll along the length and along the width of the room and reports whichever direction needs less carpet.
Worked example: a 15 × 13 ft room, 12 ft roll
- Room area: 15 × 13 = 195 sq ft; with 10% extra, 214.5 sq ft = 23.8 sq yd.
- Roll running along the 15 ft length: the 13 ft width needs ⌈13 ÷ 12⌉ = 2 strips, so 2 × 15 = 30 ft.
- Roll running the other way: the 15 ft length needs 2 strips of 13 ft, so 26 ft, which is shorter.
- Roll length to order: 26 linear ft = 312 sq ft (34.7 sq yd), with a seam to match.
This shows why a simple area calculation can under-buy: the room needs 23.8 sq yd of floor covering, but 12 ft of roll width means you pay for 34.7 sq yd.
Carpet needed for common rooms (12 ft roll, 10% extra)
| Room | Area (sq ft) | Square yards with 10% | Linear ft of roll | Leftover (sq ft) |
|---|---|---|---|---|
| 10 × 10 ft | 100 | 12.2 | 10 | 20 |
| 10 × 12 ft | 120 | 14.7 | 10 | 0 |
| 12 × 12 ft | 144 | 17.6 | 12 | 0 |
| 12 × 15 ft | 180 | 22.0 | 15 | 0 |
| 14 × 16 ft | 224 | 27.4 | 28 | 112 |
| 15 × 20 ft | 300 | 36.7 | 30 | 60 |
| 20 × 24 ft | 480 | 58.7 | 40 | 0 |
Buying tips
- Measure at the widest points and include closets, doorways and any bay.
- Plan seams. Keep them away from high-traffic spots and across the doorway if possible. Seams should run in the pile direction.
- Allow for pattern repeat. Patterned carpet needs extra to line up the design; the repeat length is given on the sample.
- Keep the offcuts. The leftovers are useful for closets, stairs or later repairs.
Stairs
Stairs are carpeted by treads and risers, not by area. A rough way to estimate is to add each tread depth plus riser height and the nosing overhang, multiply by the step width and add them up. Use the Stair Calculator for the counts.
Compare with other floor coverings using the Flooring Calculator, convert area units with the Square Yards Calculator, and measure odd shapes with the Square Footage Calculator. Roll width and board length conversions are covered by the Linear Feet to Square Feet Calculator.
Frequently asked questions
How many square yards of carpet do I need?
Multiply room length by width in feet to get square feet, add 10%, then divide by 9. A 12 × 10 ft room is 120 sq ft, which is 13.3 sq yd, or 14.7 with 10% extra.
Why do I need to buy more than the room area?
Carpet is sold in fixed-width rolls, usually 12 ft, so you pay for the full width even if the room is narrower. Seams, pattern matches, stairs and the direction of the pile add to this.
How wide is a roll of carpet?
The standard broadloom roll is 12 feet wide in North America. 15 ft rolls and 13 ft 6 in rolls exist for some styles, and 6 ft is common for cut-pile carpet tiles and for the cheaper sections of roll.
Which direction should the carpet run?
The calculator tests running the strips along both walls and gives the shorter roll length. In practice, the pile direction and the main line of sight also matter, and seams should avoid the doorway.
Does this include padding?
Pad is sold by the square yard or in rolls. Buy the room area (with a small allowance) in pad, not the extra roll waste, since pad has no seam or pattern issues.