Room Size Calculator: Square Metres and Square Feet

Type your room's width and length. The calculator gives the floor area in square metres and square feet, the perimeter for skirting, the volume, and what the size means next to UK standards and averages. It also handles an L-shaped room and a bay window. Switch to inches for feet; the common sizes fill in with one tap.

The formula, written out

A rectangle: area = length × width. 3.5 m × 4 m = 14 m². In centimetres, divide by 10,000: 350 × 400 = 140,000 cm² = 14 m².
An L-shaped room: split it into two rectangles, A and B, and add them. Every L splits this way.
A square bay: add width × depth. A bay 200 cm wide and 60 cm deep adds 1.2 m².
An angled bay (sides at 45°, the usual British bay): add (width at the wall + width at the front) ÷ 2 × depth. The front is the wall width less twice the depth.
Square feet: m² × 10.764. Square metres: sq ft × 0.0929. One foot is exactly 0.3048 m, so one square foot is 0.0929 m².
Perimeter (for skirting, coving or a picture rail): add every wall. A 3.5 × 4 m room has 2 × (3.5 + 4) = 15 m of wall.
Volume (for a heater or a dehumidifier): floor area × ceiling height. 14 m² × 2.4 m = 33.6 m³.

Split an L into two rectangles: a 4 × 5 m room with a 1.5 × 2 m part is 20 + 3 = 23 m². Sizes in cm.

An angled bay: average the two widths, then multiply by the depth. This one adds 0.84 m². Sizes in cm.

Common room sizes in metres and feet

The table gives each size both ways, with its floor area and perimeter. The last column says where it sits against the figures in the next section.

Metres	Feet	m²	sq ft	Perimeter	What it is, roughly
2 × 2	6 ft 7 in × 6 ft 7 in	4.0	43	8 m	Store room, cloakroom, small bathroom
2 × 2.5	6 ft 7 in × 8 ft 2 in	5.0	54	9 m	Box room
2.4 × 2.7	7 ft 10 in × 8 ft 10 in	6.5	70	10.2 m	Box room
2.5 × 3	8 ft 2 in × 9 ft 10 in	7.5	81	11 m	Single bedroom, at the standard's minimum
3 × 3	9 ft 10 in × 9 ft 10 in	9.0	97	12 m	Single bedroom on paper; a double bed fits
3 × 3.5	9 ft 10 in × 11 ft 6 in	10.5	113	13 m	Small double, still a single on paper
3 × 4	9 ft 10 in × 13 ft 1 in	12.0	129	14 m	Double bedroom, or a small living room
3.5 × 3.5	11 ft 6 in × 11 ft 6 in	12.25	132	14 m	Double bedroom
3.5 × 4	11 ft 6 in × 13 ft 1 in	14.0	151	15 m	Main bedroom, or a small living room
4 × 4	13 ft 1 in × 13 ft 1 in	16.0	172	16 m	Living room, just under the new-build average
4 × 4.5	13 ft 1 in × 14 ft 9 in	18.0	194	17 m	Living room, just over the new-build average
4 × 5	13 ft 1 in × 16 ft 5 in	20.0	215	18 m	Generous living room
5 × 5	16 ft 5 in × 16 ft 5 in	25.0	269	20 m	The average 1970s living room
5 × 6	16 ft 5 in × 19 ft 8 in	30.0	323	22 m	Open-plan kitchen and living room

US and older British plans give rooms in feet:

Feet	Metres	sq ft	m²
8 × 10	2.44 × 3.05	80	7.4
10 × 10	3.05 × 3.05	100	9.3
10 × 12	3.05 × 3.66	120	11.1
11 × 12	3.35 × 3.66	132	12.3
12 × 12	3.66 × 3.66	144	13.4
12 × 14	3.66 × 4.27	168	15.6
12 × 15	3.66 × 4.57	180	16.7
14 × 16	4.27 × 4.88	224	20.8
15 × 20	4.57 × 6.10	300	27.9
20 × 20	6.10 × 6.10	400	37.2

Quick conversions: 5 m² = 54 sq ft, 10 m² = 108 sq ft, 15 m² = 161 sq ft, 20 m² = 215 sq ft, 25 m² = 269 sq ft, 30 m² = 323 sq ft, 50 m² = 538 sq ft and 100 m² = 1,076 sq ft. The other way: 100 sq ft = 9.3 m², 150 sq ft = 13.9 m², 200 sq ft = 18.6 m², 500 sq ft = 46.5 m² and 1,000 sq ft = 92.9 m².

What a room size means in the UK

A number of square metres means little on its own. These are the figures UK rules and surveys give, smallest first. The calculator tells you which one your room is closest to.

Floor area	What it is	Source
4.64 m² (50 sq ft)	The smallest bedroom for a child under 10 in a licensed HMO. No smaller room may be used as a bedroom.	HMO Regulations 2018
6.51 m² (70 sq ft)	The smallest bedroom for one adult in a licensed HMO	HMO Regulations 2018
7.5 m² (81 sq ft)	A single bedroom in a new home, at least 2.15 m wide	Space standard, 2015
10.22 m² (110 sq ft)	The smallest bedroom for two adults in a licensed HMO	HMO Regulations 2018
11.5 m² (124 sq ft)	A double bedroom in a new home. The main double is at least 2.75 m wide, any other 2.55 m.	Space standard, 2015
13.4 m² (144 sq ft)	The average bedroom in a home built since 2010	LABC Warranty, 2018
17.1 m² (184 sq ft)	The average living room in a home built since 2010	LABC Warranty, 2018
24.9 m² (268 sq ft)	The average living room in a 1970s home	LABC Warranty, 2018
58 m² (624 sq ft)	The average purpose-built flat in England	English Housing Survey 2018-19
94 m² (1,012 sq ft)	The average home in England	English Housing Survey 2018-19

Two cautions. The space standard applies to new homes in England, and only where the council has adopted it or the home was made under permitted development; it is not a law for the home you live in now. The HMO sizes apply to licensed shared houses. Both are useful yardsticks all the same. The HMO figures also match, almost exactly, the 50, 70 and 110 sq ft bands in the Housing Act 1985's overcrowding test. LABC Warranty's averages come from 10,000 sale listings, not from measured rooms. For the whole home, the home size calculator checks your home against the space standard.

How to measure a room

Measure at floor level, skirting to skirting. That is the floor you can use, and the size a carpet fitter needs. A laser measure is quickest; with a tape, ask someone to hold the other end.
Measure each side twice, near both ends. Old walls are rarely square. If the two figures differ, use the larger for buying flooring and the smaller for fitting furniture.
Work in centimetres, and convert at the end. Rounding each side to the nearest half metre can change a 12 m² room by more than 1 m².
Take out a chimney breast, and add alcoves and bays as their own rectangles.
Sketch the room, and write each measurement on its wall. Mark the doors and windows too: you need them for skirting and paint.

Common mistakes

Converting area with the length factor. 12 m² is not 12 × 3.28 = 39 sq ft. An area needs the factor twice: 12 × 10.764 = 129 sq ft.
Adding the sides instead of multiplying them. 12 ft + 12 ft = 24 ft is the half perimeter. The area is 12 × 12 = 144 sq ft.
Using the longest length and the widest width of an L. That counts the missing corner as floor. Split the room first.
Mixing feet and metres. Estate agents often give both, rounded. Convert one way, once, from the most exact figure you have.
Trusting the listing. Agents often measure into bays and alcoves, which makes a room sound bigger than its usable floor. Measure it yourself before you buy furniture.

Carpet, flooring and skirting

Most domestic carpet comes off a 4 m or 5 m wide roll, sold by the metre. So the floor area is not what you buy. A 3.5 × 4 m room is 14 m², but one piece off a 4 m roll, with 10 cm spare at each side for trimming, is 4 × 4.2 m: 16.8 m². If the room is wider than 5 m both ways, the carpet needs a join. The calculator picks the cheapest one-piece cut either way round. A fitter may plan a cleverer cut, so ask for a quote before you order.

For skirting, take the perimeter and subtract the doorways: a standard UK internal door is 762 mm wide. DIY stores sell MDF skirting in 2.4 m lengths; skirting makers sell 3.05 m and 4.2 m. A wall under 4.2 m long can take one piece with no join. For laminate or vinyl planks, sold in packs of so many m², start from the floor area and follow the maker's advice on spare for cutting.

Plan the room once you know its size

Each of these guides takes one common room size and lays it out with real furniture sizes, in cm:

3 × 3 m bedroom layouts: a double bed in 9 m².
3 × 4 m living room layouts: sofa, TV and walkway in 12 m².
4 × 4 m living room layouts: 16 m², just under the new-build average.
12 × 12 ft living room layouts: 144 sq ft, in feet and cm.

Know your real sizes

Snuug, the iPhone room app, rebuilds your room in 3D from one slow walk round it. Snuug measures every wall for you when it rebuilds your room, so you know your real sizes: the length of each wall, the floor area, and where the doors and windows sit. Your room comes to within about 3% of its real size in our tests of ten homes, and our team checks every room by hand. Then move every piece in 5 cm steps and see what fits before you buy.

Questions

How many square feet is a 12x12 room?

144 sq ft: 12 × 12 = 144. In metric that is 3.66 × 3.66 m, or 13.4 m², about the size of the average bedroom in a British home built since 2010 (13.4 m², LABC Warranty).

How do I convert m² to square feet?

Multiply by 10.764. So 10 m² is 108 sq ft and 20 m² is 215 sq ft. To go back, multiply square feet by 0.0929: 100 sq ft is 9.3 m². Never convert by 3.28 for an area: that factor is for lengths, and an area needs it twice (3.28 × 3.28 = 10.76).

How do I work out the square metres of a room?

Measure the length and the width in metres, skirting to skirting at floor level, and multiply them. A room 3.6 m by 4.2 m is 15.12 m². If you measure in centimetres, multiply and divide by 10,000: 360 × 420 = 151,200 cm², which is 15.12 m².

How do I measure an L-shaped room?

Split it into two rectangles with an imaginary line, measure each one, and add the two areas. A 4 × 5 m room with a 1.5 × 2 m part is 20 + 3 = 23 m². Do not multiply the longest length by the widest width: that counts floor that is not there.

What size is a double bedroom in the UK?

For new homes in England, the nationally described space standard counts a double bedroom from 11.5 m², and the home's main double must be at least 2.75 m wide (other doubles 2.55 m). It is a planning standard for new homes, not a law for existing ones. A 3 × 4 m room (12 m²) passes; a 3 × 3 m room (9 m²) counts as a single.

What is the average living room size in the UK?

About 17.1 m² (184 sq ft) in homes built since 2010, by LABC Warranty's 2018 study of 10,000 listings. Living rooms in 1970s homes averaged 24.9 m². A 4 × 4.3 m room is close to today's average.

Editorial notes

Written by the Snuug team and checked on 1 November 2026. A number with no source beside it is a designers' rule of thumb, not a study.

Use this from an AI assistant

This answer as JSON, or as one paragraph with format=text: https://snuug.app/api/v1/tools/room-size

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