How it works
The calculator divides the room’s width across the strips by the roll width to find the number of strips, then multiplies by the strip length to get the length cut from the roll.
Strips = ⌈ Side across the strips ÷ Roll width ⌉
Length cut from the roll = Strips × Side along the strips × (1 + Extra ÷ 100)
Carpet to buy = Length cut from the roll × Roll width
Seams = Strips − 1
⌈ ⌉ means rounding up to the next whole strip: a room that is even slightly wider than the roll needs a second strip.
The amount to buy is shown in square yards (1 sq yd = 9 sq ft) because that is how carpet is usually priced in the US; switch to metric for square meters. Without a roll width, only the floor area is shown.
Worked example
Inputs
- Room length
- 15 ft
- Room width
- 12 ft
- Roll width
- 12 ft
- Strips run along
- The room length
- Extra length
- 0 %
Result
- Floor area
- 180 sq ft
- Strips
- 1
- Length cut from the roll
- 15 ft (5 yd)
- Carpet to buy
- 20 sq yd (180 sq ft)
- Seams
- 0
Common mistakes
- Paying for the floor area only. Carpet is cut from a roll of fixed width, so a room wider than the roll needs a second full-width strip even if only a narrow piece of it is used.
- Measuring at one point only. Walls are rarely perfectly straight – measure at the widest point and into doorways the carpet should cover.
- Ignoring the direction of the strips. Running them the other way can change the number of strips and seams, and the amount you buy.
- Forgetting that carpet is priced per square yard in the US. One square yard is 9 sq ft – compare prices per the same unit.
Assumptions and limits
- The room is a rectangle. For L-shaped rooms, work out each rectangle separately or ask your installer for a cut plan.
- Every strip runs the full length of the room in one direction; leftover pieces are not reused to fill gaps.
- The extra length you enter is added to the strips for trimming. Pattern matching and stairs are not modelled.
- Padding, tack strip, seam tape and transitions are not included.
Frequently asked questions
Why do I have to buy more carpet than my floor area?
Carpet comes off a roll of one fixed width. If the room is wider than the roll, you need a second strip at full roll width, and the part of it that does not fit the room is offcut. The “carpet to buy” figure is the strips you actually cut from the roll.
How do I convert square feet to square yards?
Divide by 9, because one square yard is 3 ft × 3 ft. For example, 180 sq ft is 20 sq yd. The result shows square yards first, with square feet as an alternative unit.
Which way should the strips run?
Try both settings and compare the strips, seams and amount to buy. Seam placement and the direction of the pile also matter for how the room looks, so talk to your installer before you order.
What roll width should I enter?
The one listed for the carpet you are buying. Widths vary by product – Shaw lists both 12 ft and 15 ft broadloom products – so check the specification or ask the retailer.
Sources
- Solidify II 12′ and Sophistication 15′ broadloom carpet – product specifications — Shaw Floors. US broadloom carpet is sold in fixed roll widths, e.g. 12 ft and 15 ft products; the width is listed per product.
- Broadloom vs. carpet tiles: which should you choose? — ITC (carpet manufacturer). Broadloom carpet comes in rolls 4–5 m wide.
- NIST Handbook 44, Appendix C – General Tables of Units of Measurement — National Institute of Standards and Technology. Exact unit definitions: 1 in = 2.54 cm, 1 yd³ = 27 ft³, 1 US gal = 231 in³, 1 lb = 0.45359237 kg.
Method reviewed November 2, 2026