How to Measure for Carpet: Room Size, Roll Width and Square Yards

Measure each room wall to wall in feet and inches, add closets as separate rectangles, then add about 10% (a common allowance, not a standard). Divide square feet by 9 for square yards. Most carpet comes on 12 ft rolls.

A 13 × 14 ft room is 182 sq ft, or 20.2 sq yd. Cut from a 12 ft roll it takes 26 linear feet of carpet (312 sq ft). From a 15 ft roll it takes 13 linear feet (195 sq ft). The roll width changes the order more than the waste percentage does.

How do you measure a room for carpet?

1. Measure the length and width wall to wall in feet and inches. If the walls are not square, measure at several points and use the largest figure (Flooring Clarity).
2. Treat each closet, hallway and alcove that gets carpet as its own rectangle, and measure it the same way. For an L-shaped room, split it into rectangles.
3. Write inches down as inches: 12 ft 6 in is 12.5 ft. Do not round the room itself. Round up only when you order.
4. Multiply length by width for each rectangle and add them. The square feet guide covers triangles, circles and bay windows.
5. Divide the total by 9 to get square yards, because carpet is commonly sold by the square yard and 1 square yard is 9 square feet. The square feet to square yards guide has the conversion table.
6. Ask the retailer or installer which way the carpet will run and where the seams go before you settle on a number. They lay out the room.

How much carpet do I need?

area (sq ft)      = sum of length × width for each rectangle
square yards      = area ÷ 9
order, simple     = area × (1 + allowance) ÷ 9     (allowance about 10%, a convention)
order, by roll    = strips × strip length          (strips = ceil( width across the roll ÷ roll width ))

There are two ways to size an order. The first is the area method that most retailer guides describe: net area, plus a 10% allowance, divided by 9, rounded up to the next quarter or half yard per the supplier’s rules. The second is the roll method, which is how carpet is actually cut. Carpet comes in rolls of a fixed width, so you buy a length of roll. Each strip is as wide as the roll and as long as the room, and whatever the room does not use of the strip is waste.

How wide is a roll of carpet?

Most broadloom carpet is made 12 ft wide. Shaw Floors says “most carpet is manufactured in 12-foot rolls, although 15-foot rolls are available as well”, and BuildDirect lists 15 ft and 13 ft 6 in as other widths. A U.S. Department of Veterans Affairs guide specification offers broadloom in four minimum usable widths. The roll width of the carpet you pick is on its spec sheet or the retailer’s sample, and that figure wins.

The VA specification calls these “minimum usable” widths, so the usable width is a little under the nominal one. Carpet roll width is not set by a standards body,, and not every line comes in every width.

Worked example: a 13 × 14 ft room on three roll widths

• Net area: 13 × 14 = 182 sq ft, which is 182 ÷ 9 = 20.22 sq yd.
• Area method: 182 × 1.10 = 200.2 sq ft, and 200.2 ÷ 9 = 22.24 sq yd, so 22.25 sq yd at a quarter-yard step.
• Roll method, 12 ft roll. With the 13 ft side across the roll, ceil(13 ÷ 12) = 2 strips × 14 ft = 28 linear feet (336 sq ft). With the 14 ft side across, 2 strips × 13 ft = 26 linear feet (312 sq ft). Either way there is 1 seam.
• Roll method, 15 ft roll. Either side fits in one strip, and the shorter cut puts the 14 ft side across the roll: 1 × 13 ft = 13 linear feet (195 sq ft), no seam.
• Roll method, 13 ft 6 in roll. Also one strip of 14 ft = 14 linear feet, which is 13.5 × 14 = 189 sq ft, no seam.

Carpet bought is roll length × roll width, and cut-off waste is carpet bought minus the 182 sq ft of floor. On a 12 ft roll, a room 13 ft wide leaves a second strip that is mostly offcut. Price per square yard differs by product and by width, and this guide does not know it, so compare quotes for the widths the line comes in. A wider roll is not automatically cheaper: it buys fewer seams and less waste, but you pay for the full width of the cut.

A simpler room shows the same effect. A 12 × 15 ft room is 180 sq ft, or 20 sq yd, and 180 × 1.10 = 198 sq ft is 22 sq yd on the area method. On a 12 ft roll with the 12 ft side across, you need 1 strip × 15 ft = 15 linear feet (180 sq ft). With the 15 ft side across, ceil(15 ÷ 12) = 2 strips × 12 ft = 24 linear feet (288 sq ft), a seam and 108 sq ft of offcut. In a room exactly as wide as the roll, nothing is left for trimming, and walls are rarely square, so ask your installer.

How much extra carpet should you order?

None of these figures comes from a standards body. They are retailer and editorial guidance, so treat them as typical allowances to adjust for your job.

The 10% default in this guide is the middle of those figures. If you work out the roll length, the roll-width waste is already inside that length, so a further margin on top is a judgment call. Shaw adds that a larger room may need extra material for seaming, and a large pattern repeat needs more material to match the pattern. The sources opened for this guide give no number for either. Your installer does.

What about seams and pile direction?

Carpet pile has a direction, and all strips in a room run the same way, so a strip cannot be turned to save material. Keep seams away from focal points and in low-traffic areas where you can (BuildDirect, Flooring Clarity). A U.S. Department of Veterans Affairs specification says to run side seams toward the light where practical, and to use a minimum of seams. The installer decides the layout. Ask for a seam plan before you order, and whether the carpet will run through doorways in one piece.

Assumptions, common errors and limits

• Roll widths, allowances and yard rounding are conventions and vary by product and supplier. The product’s spec sheet and your installer’s layout win.
• Dividing by 3 instead of 9. One square yard is 3 ft × 3 ft, which is 9 sq ft. Dividing square feet by 3 gives three times too many yards.
• Ordering by area only. Carpet is cut from a roll. A narrow room can cost a whole extra strip, as the 13 ft room on a 12 ft roll shows.
• Rounding the room before you measure. Measure to the inch, then round up the order.
• Leaving out closets and halls. Add every carpeted rectangle. Measure closets separately.
• Pad (cushion) is commonly estimated at the carpeted floor area, but no source opened for this guide gives a rule. Check the pad maker’s instructions.
• Stairs, landings, pattern repeat and bullnose steps need their own measurements. See how to measure stairs for carpet.

Common questions