Carpet Calculator

How this calculator works

Broadloom carpet is the odd one out among floor coverings: it comes off the roll at a fixed width and you buy it by the running length, not by loose square footage. So the real question is not the room’s area - it is “how many linear yards of this roll width do I need once the strips are laid and seamed”. For each room the calculator lays strips the roll-width wide and works out the run:

strips (along length) = ceil( room width  ÷ roll width )   → run = strips × room length
strips (along width)  = ceil( room length ÷ roll width )   → run = strips × room width
linear run            = the shorter of the two (Auto), summed across rooms
to buy                = linear run × wastage
carpet area           = run to buy × roll width

A room no wider than the roll drops in as a single seam-free piece. A wider room needs a second strip and a seam, and the leftover of that strip is carpet you still pay for - the price of a fixed roll width. The runs are summed per room because pile direction and seam visibility mean offcuts do not carry between rooms the way plank flooring does.

Stairs are the special case. A flight is carpeted with one continuous runner that wraps each step, so the carpet length is the number of steps times the tread plus the riser, and it always runs down the flight in one piece - you cannot seam across the steps. Add a staircase in the calculator and it works the runner out and pools it with your rooms. For more on each part of the job, see how much carpet do I need, how to measure stairs for carpet, and how much carpet costs.

Worked example

This example follows the unit system you pick in the calculator above.

A 16 ft × 13 ft living room on a 12 ft broadloom roll, 10% wastage:

1. The room is 13 ft wide, wider than the 12 ft roll, so one strip will not cover it.
2. Run the strips along the width: ceil(16 ÷ 12) = 2 strips, each 13 ft long.
3. Linear run: 2 × 13 = 26 ft = 8.7 linear yards, with 1 seam.
4. Add 10% wastage: 8.7 × 1.10 ≈ 9.6 linear yards to buy.
5. At 12 ft (4 yd) wide that is about 38.2 sq yd of carpet for a 23 sq yd floor - the offcut is the price of a fixed roll width.

Standard carpet roll widths

The roll width decides how many strips - and seams - a room needs, so it matters more than any other input. These are the widths you are likely to be offered:

A broadloom metre is a 1 m length cut from the full roll width - 3.66 m² of carpet from a 3.66 m roll - and is usually the smallest amount you can buy. For the full picture see standard carpet roll widths and how carpet is sold.

Tips for measuring and ordering carpet

• Measure each room at its widest points, including doorway recesses and bay windows the carpet has to reach into - a tape that stops at the wall line under-measures the run.
• Keep the pile direction the same across the whole floor; carpet looks a different shade when the nap leans toward or away from the light, and mismatched offcuts show.
• Put seams out of doorways and main traffic lines where they wear and show first, and try to run the length of a hallway in one strip.
• For stairs, add a staircase in the calculator and enter the steps, tread, riser and stair width - it works the runner length out for you. See how to measure stairs for carpet if you are not sure of the step sizes.
• Order a little long and keep an offcut for repairs; a later batch of the same carpet can vary slightly in colour.

Roll widths and how carpet is sold where you are

In the United States, broadloom carpet comes in 12 ft (3.66 m) rolls, with 15 ft and occasionally 13.5 ft also made, and it is sold by the square yard (and increasingly the square foot). However it is priced, the roll arrives at a fixed width, so the figure that really matters is the running length you need at that width - a 12 ft roll yields four square yards for every linear foot you take off the bolt, so the running length is what drives the price. Set the roll width in the calculator above to match what your retailer stocks so the run is right.

For the recognised installation detail - subfloor prep, underlay, seam placement and stretching - see the CRI 105 standard for residential carpet installation.