Carpet comes off the roll in a fixed width, so the roll sets the amount, not the floor. The calculator runs strips along the longer side of the room and lays enough of them side by side to cover the shorter side. You pay for every strip at full roll width, including the trimmed edge, so the amount can be well above the floor area.
How to use this calculator
- Measure the room wall to wall at the floor. Note the longest length and the widest width, because the calculator works from those sides.
- Enter the roll width. Most carpet rolls are 12 ft wide, and the widths in common use run from 12 to 15 ft. Use the width of the roll you plan to buy, since the strip count depends on it.
- Read the Strips off the roll line. It counts the lengths you need side by side, so check it again when you try a different roll width.
- Leave Extra for pattern matching at zero for plain carpet. Under More options, raise it for patterned carpet.
- Check which unit the store uses before you compare prices. The main result is in square yards.
Worked examples
Bedroom
Size: 12 × 10 ft · Roll width: 12 ft
- Carpet to buy
- 16.0 sq yd
- Carpet to buy
- 144 sq ft
- Room area
- 120 sq ft
- Strips off the roll
- 1
Family room
Size: 16 × 14 ft · Roll width: 12 ft
- Carpet to buy
- 42.7 sq yd
- Carpet to buy
- 384 sq ft
- Room area
- 224 sq ft
- Strips off the roll
- 2
Hallway
Size: 20 × 3 ft · Roll width: 12 ft
- Carpet to buy
- 26.7 sq yd
- Carpet to buy
- 240 sq ft
- Room area
- 60 sq ft
- Strips off the roll
- 1
Carpet to buy for common room sizes and roll widths
| Room | Roll width: 12 ft | Roll width: 15 ft |
|---|---|---|
| 10 × 12 ft | 16.0 | 20.0 |
| 12 × 14 ft | 18.7 | 23.3 |
| 14 × 16 ft | 42.7 | 26.7 |
| 16 × 20 ft | 53.3 | 66.7 |
Each cell: Carpet to buy (sq yd). Inputs not in the table use the calculator's starting values.
Why the roll width sets the amount
The calculator does not buy the floor area. Each strip is the full roll width and as long as the longer side of the room, and enough strips are placed to cover the shorter side. Every strip is paid for in full, so Carpet to buy is never less than the Room area, and it is often well above it.
A room a little narrower than the roll still takes a full-width strip, so the spare width is paid for. A room a little wider needs an extra strip that covers only a sliver of the floor. The Bedroom and Hallway cards show the narrow case, and the Family room card shows the wider case.
Pad, seams and pattern
The calculator covers the carpet only. Pad, also called underlay, is usually bought for the floor area, so use the Room area line for it.
Patterned carpet needs extra because the pattern has to line up from strip to strip. A room wider than a single roll also needs seams where strips meet, and seams need more material than the strips alone show. There is no default waste, because the strips already include the trimmed edge.
How the calculation works
The calculator takes the shorter side, divides it by the roll width, and rounds up to a whole number of strips. Each strip is the roll width times the longer side. The extra for pattern matching is added as a percentage of that total, and dividing by 9 gives square yards, because a square yard is 9 square feet.
Swapping length and width gives the same result. The gap between Room area and Carpet to buy is carpet that goes to trim and offcuts. If the same room is also a candidate for laminate, that page counts boxes from the floor area and the extra for waste instead of strips.
Mistakes to avoid
- Buying the floor area. The strips needed to cover the floor are wider, so order the Carpet to buy figure.
- Forgetting closets, alcoves and stairs. Measure each of them, and agree with your installer how each will be cut.
- Forgetting hard flooring next to the carpet. A tiled bathroom or entry is a separate order, so work it out on the tile page.
- Treating the result as a price. The calculator gives an amount of carpet only. Pad, installation and removal are separate costs.
Common questions
How do I measure a room for carpet?
Measure at the floor, wall to wall, in feet. Treat an alcove or an L-shaped section as its own rectangle, then have your installer confirm the total, since they may plan the pieces differently.
How much carpet do I need for several bedrooms?
Run the calculator separately for each bedroom with the same roll width, then add the Carpet to buy results. Each room is cut from its own strips, so the total is always at least the combined floor area. Ask your installer whether connected rooms can share a single piece.
How do I convert carpet area to square feet?
To change square yards into square feet, multiply by 9. To go the other way, divide square feet by that number, since a square yard is 9 square feet. The Room area line already gives square feet.
Do patterned carpet and seams change the amount to buy?
Yes, when the carpet has a pattern or the room needs seams. Enter an extra percentage under More options, and ask your installer how much the pattern repeat adds.
What are the different types of carpet?
Carpet is sorted mostly by fiber, such as nylon, polyester, wool and olefin, and by how the surface is made, such as cut pile or loop pile. The type changes the look, feel and price, but not how much you buy. The roll width and any pattern repeat set the amount, so check the pattern before you enter an extra percentage.