Carpet Calculator

How it works

Carpet and sheet vinyl come off a roll of fixed width, so the material is bought by the running foot of roll, not by the room's area. The room is covered with drops: strips cut across the roll and laid side by side. Enough drops are needed to span one dimension of the room, and each drop is as long as the other dimension.

Every drop includes a trim allowance at each wall; the Carpet and Rug Institute's installation standard (CRI 105, 2019) calls for at least 3 inches along each wall. For patterned carpet, one pattern repeat is added to each drop so that the pattern can be matched at the seams.

The calculator lays the drops both ways, along the room's length and along its width, and by default shows the layout that needs fewer linear feet; when both need the same, the one with fewer seams, and then the one with drops along the length. CRI 105 says seams should run the length of the area where possible and that main traffic should run parallel to them, so a layout that costs a little more can still be the better one; the drop-direction setting shows each layout for comparison.

Square yards are the linear feet times the roll width, divided by 9. Pad (cushion) is estimated from the room area, since it is trimmed to the tack strip rather than cut in drops.

Formula

span          = room dimension across the drops + 2 × trim
drops         = span ÷ roll width, rounded up
drop length   = room dimension along the drops + 2 × trim + pattern repeat
linear feet   = drops × drop length × (1 + extra % ÷ 100)
square feet   = linear feet × roll width;  square yards = square feet ÷ 9
last drop     = span − (drops − 1) × roll width
pad rolls     = room area (sq yd) ÷ pad per roll, rounded up

Example

An 18 ft × 14 ft room with a 12 ft roll and 3 in of trim at each wall: drops along the 18 ft length must span 14.5 ft, which takes 2 drops of 18.5 ft, or 37 linear ft. Drops along the 14 ft width must span 18.5 ft, which also takes 2 drops, but each is only 14.5 ft, so 29 linear ft.

The 29 ft layout is chosen: 348 sq ft, or 38.67 sq yd, of carpet with one seam, and the second drop is used 6.5 ft wide. The room itself is 252 sq ft (28 sq yd), so 27.6% of the carpet bought is trimmed off. 28 sq yd of pad is 1 roll of 30 sq yd.

Assumptions and limitations

• The room is a rectangle. For L-shaped rooms, closets and hallways, plan each rectangle separately; offcuts from one area may fill another, which this calculator does not attempt.
• Every drop is cut to the full room dimension. Installers often fill a narrow strip with an offcut laid in the same pile direction, which can save material; the last-drop width shows how much of the final drop is used.
• The 3 in trim default is the minimum in CRI 105 (2019), §5.3. Pattern matching can need more than one repeat per drop; the carpet manufacturer's installation instructions govern patterned goods.
• The 30 sq yd pad roll is a typical figure, not a standard; pad rolls vary and are labelled with their coverage. Pad is estimated from the room area without allowance for seams or offcuts.
• Roll widths shown are options, not a statement of what any product is made in. The result is an estimate; it is not a substitute for a site measure by the installer or the manufacturer's instructions.

Frequently asked questions