Carpet comes off a roll of fixed width, so the width of your room decides the waste — not its area. Run it the wrong way and you can buy half as much again for the same floor.
Enter the room and the roll width. We'll work out which direction to run it, how much comes off the roll, and where the seams land.
Works in metric and US imperial — you choose at the start and can switch at any time. Every figure this calculator uses is published with its source, and the result comes with a printable order sheet. No account, no email, and nothing you type leaves your browser.
Related: Tile calculator · Skirting calculator · Paint calculator
All calculators · How to use them · The standards behind our figures
Carpet comes off a roll of fixed width, so the width of your room relative to that roll is what determines how much you buy. Run it the wrong way and you can pay half again for the same floor. A 4.2 × 3.5 m room is 14.7 m². Off a 3.66 m roll run one way it takes about 15.4 m² in a single seamless piece; run the other way the roll will not span 4.2 m, so it needs a second drop and takes about 25.6 m² — and adds a seam. Same room, two-thirds more carpet.
Broadloom widths are not universal. 3.66 m (12 ft) is the common one, but 4 m and 5 m both exist and change the answer completely. It is the single number the whole calculation turns on, so get it from the supplier rather than assuming.
Pile direction matters as much as seam position: carpet laid in opposing directions reads as two different colours under the same light, so every piece must run the same way and the fitter needs to know which. Underlay, grippers and door bars are all separate purchases — underlay is usually sold in rolls of a different width again. Measure into every doorway and alcove, because carpet runs under the door and into the reveal, and the shortfall from measuring wall-to-wall always appears at the last threshold.
Off a roll of fixed width, so you buy a length of the full roll width rather than an area. That means the shape of the room, not just its area, decides how much you need — and which direction you run it can change the quantity by half again.
3.66 m (12 ft) is the most common broadloom width, but 4 m and 5 m exist too. Ask your supplier before calculating anything, because it is the number the whole answer depends on.
Yes, as much as seams do. Carpet laid in opposing directions reads as two different colours under the same light. Every piece must run the same way, and the fitter needs to be told which way that is.
No. Underlay, grippers and door bars are all separate, and underlay is usually sold in rolls of a different width again.