How to work out how much carpet to buy
Wall-to-wall carpet is cut from a roll, so the floor area is only the starting point. What you pay for is the length of each cut times the width of the roll. Here is the math the calculator runs with the values it opens with: one 14 x 12 ft room and a 12 ft roll.
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1
Measure the room
Take the length and width at the widest points, wall to wall, and include closets. 14 x 12 = 168 sq ft of floor, or 18.7 sq yd (divide by 9).
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2
Lay the roll both ways
Run the roll along the 14 ft wall and the 12 ft width is covered by one width: no seams. Run it along the 12 ft wall instead and you need 14 ft of width, so a second strip or a fill piece. The calculator tries both and keeps the one that uses less carpet.
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3
Add trim to every cut
Installers leave about 3 inches at each end to trim into the wall. 14 ft + 6 in = a 14 ft 6 in cut.
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4
Multiply by the roll width
14.5 ft x 12 ft = 174 sq ft, or 19.3 sq yd. That is 6 sq ft (3.6%) more than the floor, which is about as good as it gets.
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5
Price the job
174 sq ft of carpet at $2.50 is $435. Pad covers the floor plus 5% for trimming: 176.4 sq ft at $0.60 is $106. Labor at $1.00 per sq ft of floor is $168. Total: $709.
Stores often price carpet per square foot on the tag and per square yard on the invoice. $2.50 per sq ft is the same as $22.50 per sq yd. Compare quotes in one unit or the other, and check that the price includes pad and labor before you compare it with another store's.
Why you buy more carpet than floor
Two rules drive the waste. First, the roll has a fixed width, most often 12 ft, with some styles at 13 ft 6 in or 15 ft. Second, every piece in a room has to run the same way. Carpet pile leans in one direction, and a piece turned 90 degrees reflects light differently and looks like a different shade.
So a room 14 ft wide cannot be covered with one 12 ft width. You need a second piece for the last 2 ft. With "Least carpet" picked, the calculator cuts that 2 ft fill from a short length of roll: a 12 ft width yields five strips 2 ft 3 in wide, laid end to end along the seam. With "No fill pieces", it buys a second full-length strip and the offcut goes in the trash, or into a closet.
Room sizes below assume a 12 ft roll, 3 inches of trim at each end of every cut and the "Least carpet" layout. Tap a size to load it.
| Room | Floor | Carpet to buy | Extra |
|---|---|---|---|
| 10 x 10 | 11.1 sq yd | 14.0 sq yd | 26% |
| 10 x 12 | 13.3 sq yd | 14.0 sq yd | 5% |
| 12 x 12 | 16.0 sq yd | 16.7 sq yd | 4% |
| 12 x 14 | 18.7 sq yd | 19.3 sq yd | 4% |
| 14 x 16 | 24.9 sq yd | 26.7 sq yd | 7% |
| 15 x 15 | 25.0 sq yd | 27.7 sq yd | 11% |
| 20 x 20 | 44.4 sq yd | 54.7 sq yd | 23% |
Notice the 10 x 10 room: it still takes a 12 ft width, so a quarter of what you pay for is offcut. The 20 x 20 room is the other bad case: the last 8 ft is too wide to fill from strips, so it takes two full widths and throws away a 4 ft strip. In a whole-house job, a good installer plans the cuts across all rooms at once and uses those offcuts in closets and halls, so a real quote can come in a little under the room-by-room total. A quote far above it is worth asking about.
Where the seams go
Seams are where carpet jobs look cheap or look right. An installer joins two pieces with hot-melt seam tape on the back, and on cut pile a good seam nearly disappears. On loop pile and Berber it is harder to hide. Some rules installers follow:
- Run seams away from the light. A seam that runs toward a big window shows less than one that runs across the light.
- Keep them out of traffic. A seam across a doorway or down the middle of a hall wears first. Put fill pieces along the walls or into closets.
- Same direction, same roll. Every piece in view should come from the same dye lot and run the same way. Buy the whole job at once.
- Ask to see the seam plan. A careful installer will sketch where every seam goes. If the cheapest bid saves carpet by putting a cross seam in the middle of your living room, it is not the cheapest.
Choosing the pad
The pad (installers say cushion) changes how carpet feels and how long it lasts. Thicker is not always better. A pad that is too soft lets the backing flex at every step, which wears out seams and can void the warranty. The Carpet and Rug Institute's general rule for most homes is cushion no more than 7/16 inch thick and no less than 1/4 inch, at about 6 pounds per cubic foot. Your carpet maker's warranty has the final word.
| Pad type | What it is | Good for |
|---|---|---|
| Bonded urethane (rebond) | Recycled foam scraps bonded into a sheet | Most rooms; the most common pad in the US |
| Prime urethane foam | A single solid foam, firmer than furniture foam | Light-traffic rooms on a budget |
| Memory foam | Slow-recovery foam, often with a moisture film | Bedrooms where softness matters most |
| Fiber | Dense felt, often from recycled fiber or carpet | Berber and loop carpet that needs a firm base |
| Rubber | Flat or waffle rubber sheet | Heavy traffic and basements, at a higher price |
On a concrete slab or in a basement, pick a pad with a moisture barrier film and a synthetic carpet, and fix any water problem first. No pad survives a wet floor.
What it costs: DIY vs. hiring an installer
HomeGuide's late-2025 survey of homeowner quotes puts installed carpet at $2 to $8 per square foot with pad and labor. Here is how that splits:
| Item | Typical price |
|---|---|
| Carpet | $1.00–$4.50 per sq ft ($9–$40 per sq yd) |
| Pad | $0.25–$1.00 per sq ft |
| Installation labor | $0.50–$1.50 per sq ft |
| Old carpet and pad removal | $0.70–$1.60 per sq ft, with disposal |
| Moving furniture | $25–$75 per room |
| Stairs, labor | $10–$25 per step, more with spindles |
| Minimum job | $75–$150 |
Tick "Tear out old carpet" and the calculator adds removal at $1.15 per sq ft, the middle of that range. For the default room, that is $193 more. Big-box stores sometimes advertise free installation; read the fine print for minimum purchases, pad requirements and extra charges for removal and furniture.
Doing it yourself saves the labor line, but carpet is not like click flooring. It has to be stretched tight onto tack strip with a power stretcher, and the seams need a seaming iron. HomeGuide notes that renting the tools costs about as much as paying an installer for a small room. DIY makes the most sense for carpet tiles, glue-down carpet in a basement, or a small room where you can live with a less-than-perfect seam. For stretched carpet in the main rooms, most people come out ahead hiring a pro and doing the tear-out and furniture themselves.
Carpeting stairs
Each step on a straight box stair takes a piece about 22 inches long: a tread of 10 to 11 inches, a riser of up to 7¾ inches and the wrap over the nose. At the code minimum width of 36 inches, four steps fit across a 12 ft roll. The calculator buys one 22 inch cut for every four steps, adds pad for each step and charges $10 per step for labor, the low end of the per-step range, since box stairs are the simple case. Stairs with open sides, spindles or a curve take more carpet and more time.
Tips from the trade
- Measure into the doorway. Carpet usually ends under the door, at the center of the jamb. Add that strip to your room length.
- Paint first. Paint walls and baseboards before the carpet goes in, and let them dry. Drips on new carpet are forever.
- Check the subfloor. Screw down squeaks and fix soft spots while the floor is bare. It will never be easier.
- Plan the transitions. Where carpet meets tile or wood, you need a metal or wood transition strip. Count them and ask what each one costs.
- Ask about door clearance. New carpet and pad can be thicker than the old. Doors may need trimming, which is often extra.
- Keep a remnant. Ask the installer to leave the largest offcut. It is the only perfect color match you will ever have for a patch.
Common questions
How many square yards of carpet do I need for a 12x12 room?
A 12x12 room is 144 square feet, or 16 square yards. Off a 12 ft roll you buy one piece 12 ft 6 in long to leave 3 inches of trim at each end, which is 150 square feet or 16.7 square yards, with no seams.
How do I convert square feet to square yards for carpet?
Divide square feet by 9, because a square yard is 3 ft by 3 ft. A 168 square foot room is 18.7 square yards. Carpet is cut from a roll, so the amount you buy is the length of the cut times the roll width, divided by 9.
Why do I have to buy more carpet than my room size?
Carpet comes in rolls 12 to 15 ft wide, and every piece must run with the pile in the same direction. A room that is not a multiple of the roll width leaves an offcut, and each cut needs a few inches of trim at the walls. Most rooms need about 5% to 25% more carpet than their floor area.
What thickness of carpet pad should I use?
The Carpet and Rug Institute says most residential carpet should go over cushion no more than 7/16 inch thick and no less than 1/4 inch, at about 6 pounds per cubic foot. Berber and other low loop carpets usually call for a thinner, firmer pad. The carpet maker's warranty spells out its own rule, and it overrides the general one.
How much does it cost to carpet a room?
HomeGuide puts carpet installation at $2 to $8 per square foot with pad and labor, or $250 to $1,100 for a 12x12 bedroom. Carpet alone runs about $1 to $4.50 per square foot, pad $0.25 to $1.00 and labor $0.50 to $1.50.
How much carpet do I need for stairs?
Plan on a piece about 22 inches long and 3 ft wide per step for a straight box stair. From a 12 ft roll you can cut four steps across the width, so a 13-step flight takes about 4 cuts, or roughly 7.3 linear feet of roll. Installers often charge $10 to $25 per step for labor.
Sources and assumptions
The cut plan is plain geometry with the installer's rules above. Prices are typical US figures checked in October 2026 and change by region, store and carpet grade. Carpet, pad and labor prices can all be edited.
- Prices (carpet $1 to $4.50, pad $0.25 to $1.00, labor $0.50 to $1.50 per sq ft; removal $0.70 to $1.60; furniture $25 to $75 per room; stairs $10 to $25 per step; $75 to $150 minimums; $250 to $1,100 for a 12 x 12 room; roll widths of 12 to 15 ft) come from HomeGuide, carpet installation cost (October 2025). Our defaults of $2.50, $0.60 and $1.00 sit inside those ranges, and removal uses $1.15, the middle of its range.
- Pad thickness and density: the Carpet and Rug Institute rule (no more than 7/16 inch, no less than 1/4 inch, 6 lb per cubic foot) as quoted by Floor Covering Weekly, "Creating Comfort Underfoot" (April 2021), which also describes the pad types. See also carpet-rug.org.
- Stairs: the 7¾ inch maximum riser, 10 inch minimum tread and 36 inch minimum width are from the 2021 International Residential Code, section R311.7. The 22 inch cut per step and four steps per 12 ft width are our estimate for a plain box stair.
- Our own rules of thumb (estimates, not from a single source): 3 inches of trim at each end of every cut; fill strips cut 3 inches wider than the gap; 5% extra pad for trimming; pad on stairs at 4.5 sq ft per step.
- Metric mode works in meters and square meters, offers 4 m and 5 m rolls (common outside the US) next to the 12 ft roll, and keeps prices in US dollars per square meter.