How to measure for carpet
Measure the longest and widest points of the room at floor level, into any bay or doorway the carpet will cover. Then decide which way the seams should run, because that decides which measurement is the length. The CRI 105 standard says seams should run the length of the area, with main traffic alongside them and not across, and not square on to a doorway.
Closets get their own measurement. So do hallways, which often end up as offcuts from the main room when an installer plans the job well, and which cost a whole extra length when one does not.
Width matters more than people expect. The moment the room is wider than the roll, you are buying a second full length, however small the gap. Ask what width the carpet you like comes in before you compare prices per yard.
A worked example
Here is a 14 by 14 foot room on a 12 foot roll, with the pile all one way. These lines come from the same formula the calculator above runs.
14 by 14 ft room, 12 ft roll, same pile direction
- Floor: 14 × 14 = 196 sq ft
- Strips: 14 ÷ 12 rounds up to 2
- Off the roll: 2 × 14.5 ft = 29 ft
- Order: 29 × 12 = 348 sq ft, or 38.7 sq yd
That is 78 percent more carpet than floor. Allow a rotated fill piece and the order drops to 24.7 square yards, at the risk of a visible change in colour where the pile meets. A 15 foot roll needs no seam at all and comes to 24.2 square yards, so it is worth asking about even at a higher price per yard. If you are weighing carpet against something else, the flooring calculator handles planks and sheet.
Carpet for common rooms
This shows why roll width matters. Look for the rooms where the 15 foot roll is the cheaper order, and the ones where it adds waste.
| Room | Floor | 12 ft roll | 15 ft roll |
|---|---|---|---|
| Small bedroom, 10 × 10 | 11.1 | 14.0 | 17.5 |
| Bedroom, 12 × 12 | 16.0 | 16.7 | 20.8 |
| Main bedroom, 14 × 12 | 18.7 | 19.3 | 24.2 |
| Square room, 14 × 14 | 21.8 | 38.7 | 24.2 |
| Living room, 16 × 12 | 21.3 | 22.0 | 27.5 |
| Large living room, 20 × 14 | 31.1 | 54.7 | 34.2 |
Mistakes that cost you carpet
- Ordering the floor area. Dividing square feet by 9 gives the floor, not the order. You pay for the roll.
- Comparing only the price per yard. A cheaper carpet on a 12 foot roll can cost more than a dearer one on a 15 foot roll if it adds a length.
- Forgetting the room's other parts. Closets and doorways can each change the cut plan.
- Seams in the wrong place. CRI 105 wants them along the main traffic and with light not striking across them. A seam square on to a door or window is the one you will see.
- Assuming pad matches the order. Pad covers the floor and is cut to fit, so it needs far less than the carpet.
Questions
How much carpet do I need for a 12x12 room?
A 12 by 12 room needs about 16.7 square yards on a 12 foot roll, against 16 square yards of floor. The extra is the 3 inches of trim at each end wall. Add closets as separate measurements.
Why do I need more carpet than my room's square footage?
You need more because carpet comes in a fixed width and you pay for the whole width. A 14 foot wide room on a 12 foot roll takes two full lengths, and the 10 feet you cut off the second one is usually waste.
How wide is a roll of carpet?
Most carpet rolls are 12 feet wide, with 13 feet 6 inches and 15 feet also sold, and some carpet comes in 6 foot widths. It depends on the product, so ask before planning your seams.
How do I convert square feet to square yards of carpet?
Divide square feet by 9. A 180 square foot room is 20 square yards. That is the floor area, though, and not the order, because carpet is sold by the width of the roll.
Can I rotate a piece of carpet to save some?
You can, but it may show. The CRI 105 standard says adjacent pieces must have the same pile direction unless otherwise specified, because a rotated piece catches the light differently. Rotated fill suits a closet better than the middle of a room.
How much carpet do I need for stairs?
Measure one step, from the back of the tread, over the nose and down the riser, and multiply by the number of steps. We found no published allowance per stair, so this calculator leaves stairs out. Ask your installer, since each one wraps differently.
This carpet order is a planning estimate from a simple strip layout for one rectangular room. Pattern matching, closets and doorways all change the cut, and final seam placement belongs to your installer. Have the supplier measure and draw a seaming diagram before you pay, and check the roll width on the label.
Sources and review
- CRI 105 standard for installation of residential carpet, Carpet and Rug Institute, 2019.
- Soft Takes Shape, Flooring 101, Floor Covering Weekly, 2018.
- Carpet calculator, Inch Calculator, no date shown, read November 2026.
Checked in November 2026. Spotted a wrong number? Report it and it goes in the corrections log.
How this is calculated
Every figure below is read from the code that produces the answer, so what is written here is what the calculator ran. The constants were last checked against their sources in November 2026.
The arithmetic
Strips and order, same pile direction
Strips = Width ÷ Roll width, rounded up. Order = Strips × (Length + 2 × Trim) × Roll width
- Strips
- Lengths of roll laid side by side
- Trim
- Allowance at each end wall, in feet
Worked through: 14 ÷ 12 rounds up to 2, 14.5 × 2 = 29 ft, 29 × 12 = 348 sq ft
Square yards
Square yards = Square feet ÷ 9
- 9
- Square feet in one square yard
Worked through: 348 ÷ 9 = 38.67 sq yd
The constants, and where they come from
TRIM_PER_WALL_INCHES
Published figureCarpet left along each wall for trimming, in inches
Applies to: Residential broadloom installation in the United States
Source: CRI 105 standard for installation of residential carpet, Carpet and Rug Institute, published 2019, read 2026-11. This source is about 7 years old, and it is the one the figure rests on.
Section 5.3 says at least 3 inches along each wall. CRI still serves this 2019 document, though trade press reported newer standards, and it could not be confirmed which is current.
COMMON_ROLL_WIDTHS_FEET
Published range, narrowedCommon broadloom roll widths, in feet
- 0
- 12
- 1
- 13.5
- 2
- 15
Applies to: Tufted broadloom carpet sold in the United States
Source: Soft Takes Shape, Flooring 101, Floor Covering Weekly, published 2018-05, read 2026-11. This source is about 8 years old, and it is the one the figure rests on.
Trade press, May 2018, and Inch Calculator gives the same three widths. Some carpet also comes in 6 foot widths. No mill spec sheet was read.
SQ_FT_PER_SQ_YD
DefinitionalSquare feet in one square yard
Applies to: Definitional, everywhere
True by definition, so there is nothing to cite. The derivation is below.
Three feet in a yard, and an area is a length times a length, so 3 × 3 = 9.
INCHES_PER_FOOT
DefinitionalInches in one foot
Applies to: Definitional, everywhere
True by definition, so there is nothing to cite. The derivation is below.
Twelve inches make a foot by definition, so the trim allowance in inches is divided by 12.
What the labels mean
- Published figure:
- taken directly from the source named beside it.
- Published range, narrowed:
- a source publishes a range and this calculator uses a representative value from it.
- Definitional:
- true by definition, like the number of inches in a foot, so there is nothing to cite.
If a figure here looks wrong, it may be. Tell us what you found and we will check it against the source and publish a correction if it needs one. How constants are chosen and how often they are reviewed is set out in our methodology.
How to use the carpet calculator
- 1
Measure the length the way the seams should run, and the width across it
- 2
Ask what width the carpet comes in and choose it
- 3
Keep the same pile direction unless your installer says otherwise
- 4
Read the square yards to order and the seams it means
- 5
Open the prices section to see the cost at the quote you were given
What this calculator assumes
Every estimate here rests on the assumptions below. Where your job differs from one of them, the figure will differ too.
- One rectangular room, with strips running along the length
- 3 inches is left along each end wall for trimming, as CRI 105 asks
- A room exactly as wide as the roll is treated as fitting with no seam, though it leaves no trim along the sides
- Plain carpet. A patterned one needs more to line the pattern up, and this cannot size that without the repeat
Pro tips
- Ask whether a 15 foot roll removes the seam in your room, even if it means more waste
- Have seams run the length of the room, and away from the window
- Keep the biggest offcut for repairs