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About this tool
Estimate carpet roll running metres, seams, offcut wastage and cost for a wall-to-wall installation.
This calculator converts a room's length and width into the running metres of broadloom carpet you have to buy off a fixed-width roll, along with the seam count and the offcut you will pay for. Because carpet is sold by the running metre from a roll of set width, the quantity depends on which way the drops run, so it evaluates both orientations and reports the cheaper one. It is built for anyone pricing a wall-to-wall installation before the roll gets cut, since cut lengths are not returnable.
Open Carpet Roll Quantity Calculator on AltFTool — it loads instantly in your browser.
Enter the values you already know.
Fine-tune the options to match your scenario.
Read the result and use it in your planning or reporting.
Reports the layout with fewer running metres and shows what the other direction would have cost.
Prints the square metres you buy but do not lay, and that waste as a percentage of floor area.
Adds underlay at 5% over floor area and gripper rod at perimeter minus doorways.
Divide the room dimension that runs across the roll by the roll width and round up — that is the number of drops. Multiply the drops by the other room dimension plus a trim allowance of about 100 mm to get the running metres to order. A 6 m × 5 m room on a 3.66 m roll needs two drops of 5.1 m, so 10.2 running metres.
Broadloom carpet is most commonly 3.66 m wide, the metric equivalent of the imperial 12 ft roll. Some mills also run 2 m, 4 m and 5 m widths, and a 4 m or 5 m roll can remove a seam in a wide room even if the price per square metre is higher.
There is no fixed percentage — the waste is whatever the roll width leaves over after the drops are cut, which this calculator computes exactly. In a room only slightly wider than the roll it can exceed 40%, while a room close to a multiple of the roll width can be under 5%. Patterned carpet adds more because every drop is cut to a whole pattern repeat.
Underlay goes under almost all stretch-fitted broadloom carpet; it cushions the pile, adds insulation and roughly doubles carpet life. Buy about 5% over the floor area so the sheets can be butted, taped and trimmed at the walls, and fit gripper rod round the perimeter except across doorways.
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