Carpet Calculator

Strips = min( ceil(L ÷ Wr) × W, ceil(W ÷ Wr) × L ), then cost = strips × Wr ÷ unit area × price

L

Length of the room, in feet

W

Width of the room, in feet

Wr

Width of the carpet roll, in feet

n

Number of strips: how many roll widths are laid side by side

p

Price per square yard, square metre or square foot, as selected

Use it before you go to the shop, because the answer decides which roll width you should be asking for. The room area tells you nothing useful on its own: the same 260 square foot room takes 26 linear feet off a 12 foot roll and 40 off a 15 foot roll, and the second is cheaper to buy and cheaper to fit even though it looks like more carpet. Narrow rooms usually work out best on the narrow roll, wide rooms on the wide one, and near-multiples are where the waste disappears — a room 24 feet across lays two 12 foot strips with nothing left over. If what you are buying is a hard floor sold by area rather than a roll, the flooring calculator in this section is the one to use.

1. A 20 ft by 13 ft room in 12 ft wide carpet at $3.50 a square yard

   1. Floor area: 20 × 13 = 260 square feet
   2. Two strips 13 feet long, 12 feet wide: 26 linear feet, 26 × 12 = 312 square feet of carpet
   3. Waste: (312 − 260) ÷ 260 = 20% — the off-cut is the 7 feet left on each strip
   4. Square yards: 312 ÷ 9 = 34.67
   5. Cost: 34.67 × $3.50 = $121.33

   This is the page's default. The 20% waste is not a figure you can talk down — it is 7 feet off the end of each 20 foot strip, and the only ways to avoid it are a wider roll or a room that is a multiple of the roll width.

2. The same carpet in an 18 ft by 15 ft room

   1. Floor area: 18 × 15 = 270 square feet
   2. Two 12 foot strips laid across the 15 foot direction, 18 feet long: 36 linear feet — but laying them the other way needs two strips of 15 feet, which is 30
   3. The calculator keeps the cheaper orientation: 30 linear feet, 30 × 12 = 360 square feet
   4. Waste: (360 − 270) ÷ 270 = 33%
   5. Cost: 360 ÷ 9 = 40 square yards, 40 × $3.50 = $140.00

   A small change in room shape, a third more waste: 15 feet is 3 feet past a 12 foot roll, and those 3 feet are thrown away on every strip. This is the room in the reference chart below, and it is the clearest case for stepping up to a 15 foot roll, where the same room takes 18 linear feet and no waste at all.

3. A 24 ft by 16 ft room at $4.25 a square yard

   1. Floor area: 24 × 16 = 384 square feet
   2. 24 feet across is exactly two 12 foot widths, so the strips are 16 feet long: 2 × 16 = 32 linear feet
   3. Carpet bought: 32 × 12 = 384 square feet — the same as the floor, so no waste
   4. Square yards: 384 ÷ 9 = 42.67
   5. Cost: 42.67 × $4.25 = $181.33

   Zero waste, and it is worth noticing why: the room is an exact multiple of the roll width, which happens by luck rather than by design. If the room were 25 feet across the same carpet would need three strips and the waste would jump to about 44%.

The geometry is exact and the price arithmetic is exact; what is estimated is the room. The page treats the floor as one plain rectangle, and carpet is laid to fit the room that is actually there — an L-shaped room, a chimney breast, a bay window or a doorway that runs into a hall all change the strip layout, and the usual practice is to fit each rectangular area separately, which wastes more than a single pass through the overall footprint would suggest. Stairs, landings and fitted wardrobes are not rectangles at all and cannot be estimated here; add them by measurement. The page picks the orientation that buys the least carpet, which is usually but not always the same as the one a fitter would choose: pile direction across a doorway, a pattern that has to match at the seam, and a seam that has to sit out of the main sightline can all force the more wasteful layout. The price is applied to the whole of what you receive, including the off-cuts, because that is how carpet is invoiced — the waste field on the results panel is there to show you what you are paying for. Not counted: underlay, gripper rod, door bars, the fitting charge, and the fact that a large room may need a seam down the middle whichever width you buy. Carpet is also sold in fixed roll lengths, so an order of 32 linear feet may have to come as two pieces with a join in them.

Why does carpet waste so much more than flooring?

Because you buy a length off a roll of fixed width, not an area. A 20 by 13 foot room needs two 12 foot wide strips 13 feet long, so you pay for 312 square feet to cover 260 — 20% waste that no amount of care removes. The figure is set by the room's dimensions against the roll width, and the only real levers are a wider roll or a different strip direction.

What widths does carpet come in?

12 feet is the standard American width and 15 feet the wide one; 4 metres and 5 metres are the standard metric widths, with 4 metres the common one. They are not interchangeable — a 4 metre roll is 13.1 feet, so a room that lays out perfectly on a 12 foot roll may waste badly on the metric one. Put the width of the roll your supplier actually stocks into the field.

How do I work out how many square yards of carpet to buy?

Multiply the linear feet you are buying by the roll width and divide by nine. A 20 by 13 foot room on a 12 foot roll takes 26 linear feet, which is 26 × 12 = 312 square feet, and 312 ÷ 9 = 34.7 square yards. Price is normally quoted per square yard in the US, so that figure times the unit price is the invoice — waste included, which is why it is higher than the room area divided by nine.

What are carpet strips?

The number of roll widths laid side by side to cover the room. A room 20 feet across needs two strips of a 12 foot roll; 25 feet across needs three. The strip count is the thing that drives the waste, because the off-cut on each strip is the difference between the strip length and the room dimension, and that length is charged on every strip.

Can I reduce the waste by choosing a different roll width?

Often, yes — that is what the reference chart below is for. An 18 by 15 foot room wastes 33% on a 12 foot roll and nothing at all on a 15 foot roll, because 18 feet is not a multiple of 12 but 15 divides the room exactly. The opposite happens too: a narrow room laid on a wide roll throws away more than it saves. Run both through the calculator before ordering.

Is carpet priced per square metre or per square yard?

Per square yard in the United States, per square metre almost everywhere else, and occasionally per square foot. The unit selector handles all three and the price is applied to the carpet you actually receive including off-cuts, because that is what the invoice covers. Watch the units when comparing quotes: a price per square metre looks about 20% higher than the same carpet priced per square yard.

• Approximate Conversions from U.S. Customary Measures to Metric — the chart behind the square yards, square feet and metres on this page — National Institute of Standards and Technology
• The International System of Units (SI) brochure — the metre and square metre the carpet length and area are reported in — Bureau International des Poids et Mesures (BIPM)