How to use the carpet calculator
- Add one row for each room with its length and width, in the unit you measured.
- Choose the roll width you plan to buy, 12 feet, 15 feet or another width. Set the direction to least carpet so the tool tries both ways in every room, or pick a direction yourself.
- Keep the 3 inch trim allowance or change it. Enter a pattern repeat under More options if the carpet is patterned, and add extra carpet if you want a margin.
- Read the square yards to order, the length cut from the roll, the seam count and the layout for each room. Copy the shopping list for your installer.
Formula
Strips = room dimension across the roll / roll width, rounded up
Strip cut length = room dimension along the roll + trim allowance (rounded up to whole pattern repeats if a repeat is given)
Carpet from the roll = strips x cut length x roll width
Square yards = square feet / 9
Seams = strips - 1
Order = carpet from the roll x (1 + extra percent / 100)
Carpet is a roll of fixed width, so you buy a length of the roll, not a plain floor area. A room wider than the roll needs two strips and a seam. The tool tries the strips along the length and along the width and keeps the layout that uses the least carpet, and the fewest seams if two layouts tie.
Worked example: three rooms from a 12 foot roll
A 15 x 12 foot living room fits one strip along the 15 foot length: 15 ft 3 in x 12 ft = 183 sq ft. A 14 x 11 foot bedroom does the same with 14 ft 3 in x 12 ft = 171 sq ft.
A 12 x 10 foot bedroom can run the strip along its 10 foot width instead, because 12 feet of length fits the roll width exactly: 10 ft 3 in x 12 ft = 123 sq ft, which beats the 147 sq ft of the other direction.
The three rooms take 477 sq ft from the roll, which is 53 square yards, for 454 sq ft of floor. The extra 23 sq ft is trim and layout waste, about 4.8 percent of the order.
A 16 x 14 foot room is wider than the roll in both directions. Strips along the width take 2 strips x 14 ft 3 in x 12 ft = 342 sq ft (38 sq yd) with 1 seam, which is better than the 390 sq ft needed along the length.
Why carpet is ordered by the roll
Broadloom carpet is manufactured in wide rolls, commonly 12 feet and 15 feet wide, and the store cuts a length from the roll for you. Because you pay for the whole width of that cut, the area you order is usually larger than the floor area, and the difference depends on how the room fits the width of the roll. A 13 foot wide room on a 12 foot roll needs a second strip just for the extra foot, so a layout that rotates the strips can save a large amount of carpet.
Layouts are also limited by the pile direction, which has to run the same way on every strip so the color looks even. For that reason, the tool lets you set the direction yourself when the room or the carpet requires it.
Seams, trim and pattern
Every strip is cut longer than the room so it can be trimmed at the walls. A few inches is typical, and you can edit the allowance. Patterned carpet adds more waste, because each strip must start at the same point in the pattern, so a strip is rounded up to a whole number of repeats. Enter the repeat in inches under More options.
Seams show less in some places than others. Installers try to keep them out of doorways and high traffic paths, and they choose where to put them with the room in front of them. Treat the seam count as a guide, and ask for a layout plan from the installer.
Padding, stairs and extras
Carpet pad is sold by the square yard and covers the floor area, not the layout area, so the shopping list shows it separately. Stairs, landings and odd shaped rooms are not handled here, and are best measured by the installer. Tack strip, seam tape, transitions and installation are separate costs.
Assumptions and limits
- Every room is a plain rectangle. Closets, bay windows and angled walls are not included unless you add them as separate rooms.
- Each room is cut from the roll on its own. The carpet left from one room is not reused in another room.
- A 3 inch trim allowance and 12 foot roll width are example starting values that you can edit.
- Pile direction rules and seam placement are decisions for you and your installer and are not enforced here.
- Pad, tack strip, delivery, tax and installation are not included in the carpet cost.
Frequently asked questions
How do I calculate how much carpet I need?
Work out how many strips of the roll width the room needs, multiply by the strip length including trim, and multiply by the roll width. Divide square feet by 9 for square yards.
How many square feet are in a square yard of carpet?
A square yard is 9 square feet, because it is 3 feet by 3 feet. Carpet is usually priced per square yard.
Why do I need more carpet than the floor area?
Rolls have a fixed width, so you pay for the full width along the length you cut. Trim allowance and seams also add to the order.
Does a 15 foot roll waste less than a 12 foot roll?
It depends on the room. A 14 foot wide room fits one strip from a 15 foot roll but needs two from a 12 foot roll. A narrower room can waste more on the wide roll.
How much extra carpet should I order?
The layout already includes a trim allowance for each strip. Some people add a margin for repairs or mistakes, which you can enter as an extra percentage.