How the Carpet Calculator Works

Measure your room at its longest and widest points, including into door recesses and bay windows and enter dimensions. The calculator returns floor area, adds a wastage allowance for cutting and fitting, then shows roll length you actually need to order based on your chosen roll width.

That last step matters because carpet is priced and cut by linear metre from a fixed width roll. A 4m x 3m room is 12 m² of floor, but from a 4m wide roll you buy a 3m cut and roll width becomes part of cost whether your room uses all of it or not.

Roll Widths, Seams and Waste

UK carpet comes on 4m and 5m rolls, with budget ranges often in 4m only. If your room is narrower than roll, one piece does the job. If it is wider, fitter joins two strips and that seam brings rules with it, pile direction must match across the join, patterns must align and seam should sit away from main traffic and run towards the main light source so it stays invisible.

Wastage allowances by situation:

• Simple rectangular rooms: 10 percent
• Rooms with bay windows, alcoves or fitted wardrobes: 15 percent
• Patterned or striped carpet needing matching: add a further 5 percent
• Stairs: around 20 percent because of cuts involved

For an L shaped room, split it into rectangles and calculate each, then let fitter plan most economical cut, since sometimes one larger piece wastes less than two neat ones.

Do Not Skip the Underlay

Underlay does more for a carpet than carpet does for itself. It absorbs foot traffic impact so pile lasts years longer, adds warmth and cuts sound. Order same area as your carpet and note that underlay comes in rolls of roughly 15 m².

The one place underlay choice really matters is over underfloor heating, combined tog of carpet plus underlay must not exceed 2.5 or system cannot push heat into the room. Standard bedroom and living room underlay at 8 to 11mm is fine everywhere else, with a firmer, denser grade better on stairs.

Gripper rods complete order at roughly room perimeter minus doorways, plus a door bar for each threshold.

What Carpet Actually Costs

Budget polypropylene twist starts around £8 to £12 per m², mid range twist and loop piles run £15 to £30 and 80/20 wool blends, traditional quality benchmark, sit at £25 to £60 per m². Professional fitting adds £4 to £10 per m², though many retailers bundle fitting deals with a minimum spend and end of roll remnants can cover a small bedroom for a fraction of the roll price.

One buying tip that saves arguments later: compare quotes on same basis. A price per linear metre from a 4m roll is four times price per square metre and mixing two makes a dear carpet look cheap.

Worked Example

A 5m x 3.6m living room in a plain twist pile:

• Area: 18 m², plus 10 percent wastage = 19.8 m²
• From a 4m roll the room needs a seam, from a 5m roll one 3.6m cut covers it
• 5m roll order: 3.6 linear metres = 18 m² of carpet with almost no waste
• Underlay: 20 m², so two 15 m² rolls with spare or ask the fitter to supply exact
• Gripper: perimeter 17.2m minus one doorway, roughly 16m plus one door bar

The 5m roll wins here even at a slightly higher price per metre because it removes the seam and the offcut entirely.