Carpet Calculator
Carpet comes off a roll of fixed width, and the pile has to run the same direction throughout a room — so what you buy depends on how the room divides into strips, not just on its area. Enter the room and the roll width, and this works out both ways the carpet can run, tells you which wastes less, and gives the linear feet to order.
Results
Why carpet is not sold like paint
Every other material on this site scales with area: twice the floor, twice the boxes. Carpet does not, because it arrives as a roll of fixed width and you buy whatever length of that roll the room forces you to buy. A 12 ft roll is the near-universal US width; 13 ft 6 in and 15 ft exist but are stocked in far fewer styles, and a mill that offers one width rarely offers the others in the same pattern.
The second constraint is pile direction. Carpet fibers lean, which is why a rug looks lighter walking one way and darker the other. Two pieces laid with their pile opposed will look like two different colors under the same light even though they came off the same roll — so every strip in a room must run the same way. That single rule is what stops you from filling a gap with an offcut, and it is the reason waste is unavoidable rather than sloppy.
Formula: strips = ceiling(room width ÷ roll width), then carpet = strips × room length × roll width
The direction you run it is the number that costs money
For any room that is not square, the carpet can run two ways, and they are rarely equal. Take a 14 × 20 ft bedroom on a 12 ft roll:
| Strips run | Strips needed | Length off the roll | Carpet bought | Waste |
|---|---|---|---|---|
| Along the 20 ft length | 2 (14 ÷ 12 rounds up) | 40 ft | 480 sq ft / 53.3 sq yd | 200 sq ft |
| Across the 14 ft width | 2 (20 ÷ 12 rounds up) | 28 ft | 336 sq ft / 37.3 sq yd | 56 sq ft |
Both give the same finished floor and both give one seam. One costs 16 square yards more than the other — at $28 a yard that is about $450 of carpet bought to be thrown away. The calculator above works out both and names the cheaper one, because a showroom quote will usually assume whichever direction the installer prefers rather than the one that buys less.
Rooms narrower than the roll are the case worth chasing hardest. A room up to 12 ft in one dimension takes a single strip with no seam and no width waste at all, which is why 11 ft 9 in bedrooms are so much cheaper to carpet than 12 ft 3 in ones.
Square yards, square feet, and the price you are actually quoted
Carpet has been sold by the square yard in the US for a century, and plenty of showrooms still quote that way; big-box retailers increasingly quote per square foot because the number looks smaller. One square yard is exactly 9 square feet, so a carpet at $3.50 per sq ft is $31.50 per sq yd — the same carpet at what sounds like a tenth of the price.
Formula: sq yd = sq ft ÷ 9
When you compare quotes, check three things beyond the headline rate: whether the price includes padding, whether it includes installation, and whether it is priced on the carpet bought or the floor covered. Those are different numbers on every room that needs more than one strip, and a quote priced on floor area with material charged on roll area is where the surprise lands.
Padding, tack strip and the rest of the order
- Padding is bought to the floor area, not the roll area. It has no pile direction, so offcuts can be pieced in freely — a padding order matching the carpet order is money spent for nothing. Most residential jobs use 8 lb density in 7/16 in thickness; check the carpet warranty, because many void above 7/16 in.
- Tack strip runs the room perimeter, less the doorways. For the 14 × 20 room that is 68 linear ft minus about 3 ft per door.
- Seaming tape is bought to the seam length. Two strips down a 20 ft room is 20 ft of tape, and it wants to be heat-bond tape, not the pressure-sensitive kind.
- Transitions at each doorway where the carpet meets a different flooring.
Stairs are a separate calculation
Do not fold stairs into the room figure. A standard step needs the tread depth plus the riser height plus about 3 inches to wrap the nosing — call it 18 to 20 inches of carpet per step, run the full width of the stair plus any waterfall over the edges. Thirteen steps at 19 in is about 21 linear feet, and because the pile must run down the flight, that length comes off the roll in one piece rather than being pieced from offcuts.
Work out the rise and run of the flight first if you do not have them, then come back with the tread and riser figures.
Frequently asked questions
How do I calculate how much carpet I need?
Divide the room width by the roll width and round up — that is how many strips you need. Multiply the strips by the room length to get the linear feet to order, then multiply by the roll width for the total square footage. Divide by 9 for square yards. Do the same calculation with the room turned 90 degrees, because one direction almost always buys less carpet than the other.
How wide is a roll of carpet?
Twelve feet is the standard width in the US and covers the great majority of styles. Some mills also produce 13 ft 6 in and 15 ft rolls, which can eliminate a seam in a wider room, but the selection in those widths is much smaller and they are not usually stocked locally.
How many square feet are in a square yard of carpet?
Exactly 9. A square yard is 3 ft by 3 ft. So carpet quoted at $3.50 per square foot is $31.50 per square yard for the identical product — worth converting before comparing two showroom quotes, because retailers do not all quote the same way.
How much extra carpet should I order for waste?
For a plain carpet the roll-width calculation already contains the waste, because you are buying full-width strips whether you need the full width or not. Add roughly 3 inches per strip for trimming, which this calculator does by default. A patterned carpet is different: you also lose one pattern repeat per seam so the design lines up, which can add 5 to 15 percent on a large repeat.
Where should a carpet seam go?
Run seams in the same direction as the main light source rather than across it, since a seam catches the eye most when light rakes across it. Keep seams out of doorways and out of the main traffic path, because that is where they take the most abuse and open up first. In a bedroom, aim the seam away from the window and under where the bed will sit if you can.
Do I need the same amount of padding as carpet?
No, and ordering it that way wastes money. Padding is bought to the actual floor area because it has no pile direction and offcuts can be pieced together. Carpet is bought to the roll area because it has a pile direction and offcuts cannot. In a room needing two strips, the padding order can be significantly smaller than the carpet order.