How Much Carpet Do I Need?

Carpet is priced and cut by the square yard, not the square foot, and — unlike tile — it can only be cut in full-width strips off a roll, which usually means buying more than the room's bare floor area. The table below shows that difference for common room sizes across both standard US roll widths. For your own room's exact dimensions, the carpet calculator computes the precise figure and picks the cheaper roll orientation automatically.

Carpet to buy by room size and roll width

Carpet is quoted in square yards. If you only need to convert a floor area, the square footage calculator gives square feet, square yards and square metres together. The table below answers the carpet-specific question: how much you actually buy once the room is fitted to a roll. Each strip is cut 3 in longer than the room dimension it spans for trimming, and each room uses whichever of its two orientations against the roll needs less material, the same method the calculator applies.

Carpet and Rug Institute and major US retailer (Lowe's, The Home Depot) installation guides: 12 ft is the standard broadloom carpet roll width sold in the US, with 13 ft 2 in and 15 ft as less common alternates — notice the 12 ft roll needs less material for every room here except the 12 × 15 ft room, where the two widths land almost the same, and the 14 × 16 ft room, where the wider 15ft roll actually wins because it avoids a second seamed strip. Which roll width is cheaper depends on whether a room's dimension crosses the roll width, not on the room's total area.

Worked example: how roll width decides whether you need a seam

Take the 14 × 16 ft room from the table. Neither dimension fits across a 12 ft roll, so on that width the room needs two strips side by side and a seam either way. The cheaper orientation runs the strips along the 14 ft dimension: two strips, each cut to 14 ft plus the 3 in allowance, give 2 × 12 × 14.25 = 342 sq ft, or 38.0 sq yd, against a floor area of 24.9 sq yd. On a 15ft roll, the room's 14 ft dimension fits across the roll in one piece, so a single strip cut to 16 ft plus the allowance covers the whole floor: 1 × 15 × 16.25 = 243.75 sq ft, or 27.1 sq yd, with no seam at all. The wider roll wastes a 1 ft strip along one side, but it still needs about 11 sq yd less carpet. A wider roll that avoids a seam can beat a narrower one even though it wastes more width, so check both before ordering, as the table and the calculator both do.

Carpeting several rooms at once

The table treats every room on its own, which is how the figures are easiest to compare. When several rooms are carpeted in one job, an installer draws a cut plan for the whole order, and offcuts from one room can cover another. The 14 × 16 ft room above is a good example on a 12 ft roll. The second strip is 12 ft wide, but the room only needs 4 ft of it, leaving an offcut about 8 ft wide and just over 14 ft long. That is enough to carpet a 3 ft wide hallway up to 14 ft long, or a closet, without buying any more carpet. Adding up per-room figures from the table would buy that hallway twice.

Offcuts are only reusable when the pile runs the same way in both spaces and the join between them falls where a seam is acceptable, such as a doorway. Treat the per-room sum as the upper limit of the order, and ask the retailer or installer for a combined cut plan before paying for it.

Narrow rooms and hallways

Hallways show the roll-width effect at its most extreme. A 4 × 20 ft hallway is 80 sq ft, or about 8.9 sq yd of floor. Cut from a 12 ft roll on its own, it needs a strip 12 ft wide and just over 20 ft long, about 27 sq yd, three times the floor area. That is why hallways are the first place to look for offcuts from bigger rooms, and why a long hallway carpeted on its own is sometimes cut from a runner or a narrower roll where the style is available in one. If the hallway is part of the same job as a large room, mention it when asking for the cut plan rather than pricing it separately.

Outside the US: widths in metres

In the UK, Ireland and much of Europe, broadloom carpet is sold by the square metre, and the common roll widths are 4 m and 5 m rather than 12 ft and 15 ft. The method is exactly the same: fit the room against the roll width, add a trimming allowance to each strip, and compare both orientations. A 4 m roll is about 13 ft 1 in wide, so a room up to 4 m across fits in one strip where the same room on a US 12 ft roll would need a seam. Rooms between roughly 4 m and 5 m across are where the 5 m roll avoids a seam. The calculator's roll-width choices are the US widths, so for a 4 m or 5 m roll, work through the same steps by hand or ask the retailer for a cut plan.

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