Carpet Calculator — Square Yards and Roll Width
Carpet comes off a 12 ft wide roll, so a room 13 ft across needs a seam and a lot more carpet than its area suggests. This tells you which side of that line you are on.
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How to work it out
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Measure the room at its widest
Measure into doorways and alcoves, not just the main rectangle. Carpet is cut from a roll and the fitter needs the widest point, because that is what the piece has to cover.
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Compare the narrow dimension to the roll
Standard carpet is 12 ft wide. A room 11 ft across is one piece with no seam. A room 13 ft across needs a second strip, and the cut-off from it is usually unusable.
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Convert to square yards
Carpet is priced by the square yard in the US — that is nine square feet. Dividing by nine is the step people forget, and it makes the price look nine times worse than it is.
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Add underlay and fitting extras
Underlay is bought to the same area. You also need tack strip around the perimeter, and door bars wherever the carpet meets another floor.
Carpet by room size
Including 10% waste. The last column is whether it fits a 12 ft roll without a seam.
| Room | Area | Square yards | With waste | Seam-free? |
|---|---|---|---|---|
| 10 × 12 ft | 120 sq ft | 13.3 sq yd | 14.7 sq yd | Yes |
| 12 × 12 ft | 144 sq ft | 16.0 sq yd | 17.6 sq yd | Yes |
| 12 × 14 ft | 168 sq ft | 18.7 sq yd | 20.5 sq yd | Yes |
| 12 × 16 ft | 192 sq ft | 21.3 sq yd | 23.5 sq yd | Yes |
| 14 × 16 ft | 224 sq ft | 24.9 sq yd | 27.4 sq yd | No |
| 15 × 20 ft | 300 sq ft | 33.3 sq yd | 36.7 sq yd | No |
| 20 × 24 ft | 480 sq ft | 53.3 sq yd | 58.7 sq yd | No |
A room whose narrow dimension is 12 ft or less takes one piece. Past that, expect a seam and more waste.
What else the job needs
| Item | How much | Note |
|---|---|---|
| Underlay | Same square yardage | 8 lb density minimum for a living area. |
| Tack strip | Room perimeter, less doorways | Sold in 4 ft lengths. |
| Door bars | One per doorway | Where carpet meets a different floor. |
| Seam tape | Length of each seam | Only if the room is wider than the roll. |
Good underlay makes a cheap carpet feel expensive and doubles its life. It is the wrong place to save money.
Why roll width decides the price
Carpet comes off a roll 12 ft wide. If your room is 11 × 14 ft, the fitter rolls out a 14 ft length of that 12 ft roll and the job is done — one piece, no seam, 18.7 sq yd.
If the room is 13 × 14 ft, that same piece leaves a foot short. You need a second strip 1 ft × 14 ft, but carpet is not sold in 1 ft widths — you buy another full-width length and bin most of it. The room is 12% bigger and the order is 40% bigger.
This is why two rooms of similar size can be quoted wildly differently.
How many square feet in a square yard?
Nine. A square yard is 3 × 3 ft.
US carpet is priced per square yard while rooms are measured in feet, which catches people out in both directions — a carpet quoted at $27 a yard is $3 a square foot, not $27.
Do not skimp on the underlay
Underlay does most of the work you attribute to the carpet. It provides the softness underfoot, it absorbs the compression that would otherwise crush the carpet fibers, and it is the reason a good carpet lasts fifteen years instead of seven.
For a living room, 8 lb density at 7/16 in. is a sensible minimum. Thicker is not automatically better — over-soft underlay lets the carpet flex too much at the seams.
Where the seam should go
If a seam is unavoidable, it should run along the length of the room rather than across it, sit away from the main walking line, and run towards the window rather than across the light. A seam lit from the side is visible; the same seam running with the light usually is not.
Tell your fitter where the main door and window are before they plan the cut.
Carpeting stairs is measured differently
Stairs are not floor area. Each step takes the tread depth plus the riser height, plus a couple of inches for the nose.
A typical step with a 10.5 in. tread and a 7.2 in. riser needs about 20 in. of carpet run, so a 15-step flight needs roughly 25 linear feet — and that is per width of stair, in one continuous piece if you want no joins.
For a 3 ft wide staircase that is about 8.3 sq yd before waste. Add 10%, and add more again if the carpet has a pattern that has to line up from step to step.
Winders and landings are cut individually and waste heavily. If your stairs turn, expect a fitter to want 20% or more.
Twist, pile and what actually wears well
The number on the label that predicts how a carpet will look in five years is density, not thickness.
Density — how tightly the fibers are packed. Bend a sample back on itself: if you can easily see the backing through the pile, it is loosely made and it will flatten in the traffic lanes. Dense carpet holds up.
Twist level — how tightly each fiber is twisted. Higher twist resists the fuzzy, matted look that makes a carpet look tired long before it is worn out.
Fiber — nylon wears best and cleans well. Polyester is softer and more stain-resistant but crushes sooner. Wool is excellent and expensive. Olefin resists moisture and is the usual choice for basements.
A dense mid-priced nylon over good underlay outlasts a thick cheap carpet over thin underlay, comfortably.
How this is worked out
No black box — here is the arithmetic the calculator runs, so you can check it against your own numbers.
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area = length × width, summed over every sectionMeasure into doorways and alcoves. -
× (1 + waste ÷ 100)10% plain, 15% for a pattern that must match across a seam. -
× 1.1 again if the room is wider than the rollA seamed room wastes most of the second strip. -
square yards = square feet ÷ 9US carpet is priced per square yard. -
seam check: narrow dimension > roll width12 ft is the standard roll. Wider rooms need a second strip.
Common questions
How many square feet in a square yard of carpet?
Nine. A square yard is 3 × 3 ft. Divide your square footage by nine to get the yardage carpet is priced in.
How wide is a roll of carpet?
Twelve feet is the US standard. Fifteen feet exists and is worth asking about for wide rooms, because it can eliminate a seam. Some imported carpet comes in 4 m, about 13.5 ft.
Why does my room need a seam?
Because it is wider than the roll. A room more than 12 ft across its narrow dimension cannot be covered by one piece, so a second strip is joined on — and most of that strip is waste.
How much extra carpet should I order?
Ten per cent for a plain carpet, fifteen for a pattern that has to be matched across a seam. Your fitter may want more depending on the layout.
Do I need new underlay?
Almost always. Old underlay is compressed where the furniture and walkways were, and reusing it under new carpet wastes the carpet. It is a small part of the total cost and it determines how the floor feels.
What underlay density should I choose?
8 lb density at about 7/16 in. for a living area; 6 lb is acceptable for a bedroom. Thicker is not automatically better — over-soft underlay flexes at the seams and shortens the carpet's life.
Should I measure into doorways?
Yes. Carpet runs into the doorway and finishes under the door, so those few inches are part of the piece the fitter has to cut.
Can I install carpet myself?
A small bedroom, possibly. Anything needing a seam or a stretcher, no — carpet has to be stretched properly or it ripples within a year, and the tools to do it are not worth buying for one room.
Where these figures come from
Every figure below is traceable. How we check the numbers explains how they are verified, and the coverage reference collects them all in one place.
- Carpet and Rug Institute CRI 105 — installation standards, seam placement and underlay requirements
- Manufacturer roll specifications — standard 12 ft and 15 ft roll widths
- Underlay density guidance — minimum density and thickness by traffic level
Think a number here is wrong? Tell us — we check every report, correct the page, and date the change. Last checked September 11, 2026.