How much carpet for a 4 m × 4 m room?
21 m² a piece 5 m × 4.2 m
A 4 × 4 m room needs a piece of carpet 5 m × 4.2 m, cut from the 5 m wide roll: 21 m², with no join. The floor itself is only 16 m². The rest is the trimming allowance and the roll's fixed width.
The catch is the roll. A room exactly as wide as the narrower stock roll leaves the fitter nothing to trim, so the sum moves up to the wider roll and you pay for a strip you will not see. A room even a little narrower drops back to the narrower roll and costs noticeably less.
So measure wall to wall at the widest point, into any door recess, and try your exact figure in the calculator. Ask the shop what trimming allowance its fitters want: some work with less than this page allows.
Worked out for A plain rectangular room 4 × 4 m (13 ft 1 in × 13 ft 1 in), carpeted in one piece with a little extra on every side for trimming. Change the numbers
The working
- Floor: 4 m × 4 m = 16 m²
- Carpet comes off a roll of fixed width, and the piece must be wider and longer than the room so the fitter can trim it to the walls.
- The cheapest single piece here is 5 m × 4.2 m, off the 5 m roll, with no join.
- That piece is 21 m² (226 sq ft), and you pay for all of it.
The rule, and its source
UK carpet roll widths
Most domestic carpet in the UK is made in 4 m and 5 m widths and sold by the metre off the roll.
Shop sizes Source: Flooring Hut, What widths do carpets come in? (checked 31 October 2026).
Other room sizes
The cheapest one-piece cut for each room, off whichever stock roll width covers it.
| Room | Piece to buy | Area you pay for |
|---|---|---|
| 3 × 3 m | 4 m × 3.2 mno join | 12.8 m² |
| 3 × 4 m | 5 m × 3.2 mno join | 16 m² |
| 3.6 × 4.2 m | 4 m × 4.4 mno join | 17.6 m² |
| 4 × 4 m this page | 5 m × 4.2 mno join | 21 m² |
| 4 × 5 m | 5 m × 5.2 mno join | 26 m² |
| 4.5 × 5 m | 5 m × 5.2 mno join | 26 m² |
Change the numbers
Your sizes will differ. The room size calculator opens with these numbers filled in: change any of them and the answer, the working and the drawing follow.
Editorial notes
Worked out by the Snuug team on 12 November 2026 with the same code as the room size calculator, so the two cannot disagree. Every rule cites its source, with the date we last checked it. A rule designers use is a convention, not a study.
Other sources the calculator draws on:
- DCLG, Technical housing standards: nationally described space standard (March 2015, notes added 19 May 2016), Table 1 and paragraph 10, checked 31 October 2026
- The Licensing of Houses in Multiple Occupation (Mandatory Conditions of Licences) (England) Regulations 2018 (SI 2018/616), regulation 2, checked 31 October 2026
- Which? (Garber, 14 Apr 2018), Shrinking homes: the average British house is 20% smaller than in the 1970s (LABC Warranty analysis of 10,000 Zoopla and Rightmove listings), checked 31 October 2026
- Statista, Average living room sizes in new British houses 1930–2020 (LABC Warranty data), checked 31 October 2026
- MHCLG, English Housing Survey 2018-19, Size of English homes fact sheet, checked 31 October 2026
- B&Q, Metsä Wood primed MDF square skirting board, 2.4 m, pack of 4, checked 31 October 2026
- MDF Skirting World, The length option (3050 and 4200 mm), checked 31 October 2026
- Howarth Timber (Green, 14 Sep 2026), UK door sizes, checked 31 October 2026