Carpet Calculator

Why carpet is figured from the roll, not the floor area

Broadloom carpet comes off a roll of fixed width. Shaw says most carpet is made in 12 ft rolls and that 15 ft rolls are also available; the width filter in its carpet catalog offers only those two.^[1][2] You buy a length of roll at its full width, so what you pay for is length × roll width, not the area of your floor.

Two installation rules set that length:

• One pile direction. Where pieces of the same carpet meet, CRI 105, the carpet industry’s residential installation standard, requires the pile to run the same way (§5.2), and Mohawk’s instructions say the same.^[3][4] Mohawk’s commercial instructions even say fill pieces should be marked to show their pile direction.^[5] A narrow fill therefore can’t be cut crosswise from a scrap; it is another full-length cut off the roll.
• Trim at the walls. CRI 105 §5.3: cut “allowing at least 3 inches along each wall for trimming.”^[3] Each room dimension grows by 6 in before it is laid out.

The calculator tries the roll both ways in each room and keeps the one that uses less carpet. If both use the same amount it takes the one with less seam, and after that the one that runs along the room’s length. You can also set the direction yourself.

Example: a 14 × 16 ft bedroom

1. Add the trim: 16 ft + 6 in = 16 ft 6 in, and 14 ft + 6 in = 14 ft 6 in
2. Run the roll along the 14 ft walls, so each cut is 14 ft 6 in long. The cuts lie side by side across 16 ft 6 in: 16.5 ÷ 12 = 1.38 → 2 pieces. The second piece is a fill that uses only 4 ft 6 in of its width.
3. Carpet: 2 × 14 ft 6 in = 29 ft of roll × 12 ft = 348.00 sq ft = 38.67 sq yd
4. Left over: a piece 7 ft 6 in wide and 14 ft 6 in long

The floor is 224 sq ft, or 24.89 sq yd, so the 12 ft roll takes 55% more than the floor. On a 15 ft roll the same room is one piece 16 ft 6 in long with no seam: 247.50 sq ft = 27.50 sq yd. That is why it pays to ask whether the carpet you like comes in both widths.

The common rule of adding 10% to the floor area, which This Old House gives, misses this.^[6] For this room that rule gives 27.38 sq yd, 11.29 sq yd short of what the 12 ft layout needs. No carpet maker or CRI document we checked gives a waste percentage, so the calculator does not use one. It works from the cuts.

Where the seams go

CRI 105 §5.1 asks for as few seams as possible and, where possible, seams that run the length of the area, with main traffic running along them rather than across, out of the line of natural light, away from spots where people pivot, and not perpendicular to doorway openings.^[3] Masland’s instructions also say seams should run lengthwise, parallel to traffic paths.^[7] CRI 105 also notes that pile laid toward the entrance is ideal, though economy may decide it.^[3]

The cheapest layout isn’t always the best seam. In the 14 × 16 ft room the cheapest layout puts a 14 ft 6 in seam across the room’s 16 ft length. Turning the roll so the seam runs lengthwise takes 44.00 sq yd, 5.33 sq yd more. Set “Lay the roll” to compare, then decide with your installer where the doors, windows and walking paths are.

Rooms just over the roll width

With 3 in of trim on each side, a 12 ft roll covers a room up to 11 ft 6 in wide in one piece, and a 15 ft roll up to 14 ft 6 in. Go past that and you need a fill strip, which still costs a full-length cut:

• 11 ft 6 in × 12 ft: one piece, 16.67 sq yd
• 12 × 12 ft: a 6 in fill makes it 2 pieces, 33.33 sq yd on a 12 ft roll, or 20.83 sq yd in one piece from a 15 ft roll

So measure carefully, wall to wall at the floor, at the widest point. A room called “12 by 12” on a plan may measure a little less between the walls. The square footage calculator reads feet and inches like 11'6".

Carpet needed for common room sizes

Each row is one rectangular room worked out by the calculator with 3 in of trim at each wall and the cheaper roll direction. Leftovers are not reused.

In this table the 15 ft roll wins when the room’s short side is over 11 ft 6 in and no more than 14 ft 6 in, because it covers the room in one piece where the 12 ft roll needs two. Below that the 12 ft roll is one piece and cheaper. Above it both rolls need two pieces, and the second 15 ft piece wastes more. Neither width is always cheaper, so check both.

Leftovers, closets and several rooms

The calculator lays out each room on its own. In practice the installer’s seaming diagram (CRI 105 §5.3 says carpet is cut to it) often fits a closet or a hall into a leftover.^[3] The 14 × 16 ft room leaves a 7 ft 6 in × 14 ft 6 in piece. A 3 × 6 ft closet needs a piece 3 ft 6 in along the roll and 6 ft 6 in across it with trim, which fits inside that leftover, while entering the closet as its own room adds 4.67 sq yd. Add every room to see the most you could need, and keep the pile direction the same in pieces that meet at a doorway. Then ask your retailer to lay out the whole job before you order.

Priced per square yard or per square foot

A square yard is 9 square feet.^[8] Carpet is often priced per square yard; Mohawk’s 2012 federal price list for commercial carpet, for one, quotes it that way.^[9] NIST’s model sales regulation calls for a price per square foot when carpet is sold in U.S. units, and Shaw’s own site lists prices per square foot.^[10][2] Multiply a square foot price by 9 to compare it with a square yard price. Using example prices only, $3.00 per sq ft and $27.00 per sq yd are the same: the 14 × 16 ft room costs 348.00 × $3.00 = $1,044.00, or 38.67 × $27.00 = $1,044.00. The calculator prices the carpet you order, leftover included, not the floor area. Pad and installation are separate.

Pad, tack strip and seam tape

• Pad (cushion) covers the floor only, not the trim. Future Foam and Leggett & Platt spec sheets list rolls of 6 × 45 ft, which is 270 sq ft or 30 sq yd.^[11][12] The 14 × 16 ft room is 224 ÷ 270 = 0.83 → 1 roll. Thickness follows the carpet maker: CRI 105 says no more than 7/16 in for homes; Mohawk calls for 3/8 to 1/2 in and at least 5 lb/cu ft for cut pile, and 1/4 to 3/8 in for berber.^[3][4] CRI 105 puts pad seams at right angles to carpet seams or at least 6 in to one side.^[3]
• Tack strip runs along every wall; CRI 105 §11.1 says to avoid running it across door openings and sills. Homes use 1 in wide strip; CRI 105 requires the wider architectural strip, or two strips, where the carpet is stretched more than 30 ft.^[3][4] The calculator takes the room perimeters, subtracts the doorway widths and divides by 4 ft sticks, a length from a retail listing rather than a standard; check the pack you buy.^[13] 14 × 16 ft with a 3 ft door: 60 − 3 = 57 ft ÷ 4 = 14.25 → 15 sticks.
• Seam tape covers the seam length the calculator shows (14 ft 6 in in the example). CRI 105 and Mohawk call for tape with at least 2¾ in of adhesive width; Masland recommends 3 in tape.^[3][4][7]

Carpet for stairs

CRI 105 §15.4 recommends running the length of the roll up the stairs, and notes that most makers want the pile running down them.^[3] Stair pieces are therefore cut along the roll, and several stair-width strips come side by side off one roll width. The calculator works it like this:

For 13 steps 36 in wide, with a 10 in tread and a 7.5 in riser: each step takes 17.5 in, a 12 ft roll gives 4 strips, 13 ÷ 4 → 4 steps per strip, and 4 × 17.5 in + 2 ft = 7 ft 10 in of roll, or 10.44 sq yd. The calculator counts pad on the treads only (32.5 sq ft); CRI 105 §15.1 has the cushion run over the nose as well, so allow a little more.^[3] The strip width is the stair width you enter. For edges turned under at the sides, CRI 105 §15.2 sets the tack strip and pad about 1½ in narrower than the carpet, so enter the wider carpet width; a wider strip can mean fewer strips side by side and more roll.^[3] Count steps by the treads you will cover (a flight often has one more riser than treads).

The 2 ft is This Old House’s allowance, not a standard; neither CRI 105 nor Mohawk gives one.^[6] Open sides, landings and wrap styles change the cut, so measure a landing as its own room and have your installer check the stair plan. CRI 105 also calls for tack strip on each tread (§15.2), which the tack strip count above does not include.^[3] Carpet that comes loose on a stair is a tripping hazard, so stairs are a good place to pay for an installer.

Patterned carpet

CRI 105 says patterned carpet needs extra material for matching, and Shaw says larger rooms may need extra for seaming, but neither gives an amount.^[3][1] Makers expect patterns to stretch slightly along the roll and installers to correct it: Mohawk allows 1½ in of pattern elongation in 12 ft, Beaulieu says to be ready to correct 1 in, and Masland lists a repeat tolerance of 1% (1.44 in in 12 ft).^[4][14][7] The calculator does not add anything for a pattern, so ask the retailer for the quantity on patterned carpet.

Related calculators

• Square footage calculatorRoom areas in feet and inches, with sq yd
• Wallpaper calculatorRolls by strips, pattern repeat and trim
• Tile calculatorTiles and boxes by tile size and layout
• Project materials listPrint everything you added from each calculator

Prepared by the Yard & Build editors. The formulas behind this calculator are checked against hand-worked answers every time the site is built. Installation standards and product specs checked October 5, 2026.