How much paint for a 3 m × 3 m room?
4.4 litres 1 × 5 l · the walls, 2 coats
The walls of a 3 × 3 m room need 4 litres of emulsion for 2 coats, 4.4 litres with 10% spare: buy 1 × 5 l. One large tin does it, with a little left for touching up. With the ceiling painted too the job needs 5.9 litres: 1 × 5 l + 1 × 2.5 l.
A small bedroom or box room is a one-tin job, which makes it the cheapest room in the house to change. The large tin costs less per litre than two small ones, so buy the large one even though the sum comes in under it.
The sum takes out 1 door and 1 window. A room with fitted wardrobes along a wall has less to paint than this, so take that wall's width off in the calculator before you buy.
Worked out for The four walls of a room 3 × 3 m (9 ft 10 in × 9 ft 10 in) with a 2.4 m (7 ft 10 in) ceiling, less 1 door and 1 window, with 2 coats of emulsion that covers 13 m² a litre. Change the numbers
The working
- Walls: 2 × (3 m + 3 m) × 2.4 m = 28.8 m²
- Less 1 door at 1.51 m² and 1 window at 1.44 m²: −2.95 m²
- Area to paint: 25.9 m²
- 25.9 m² × 2 coats ÷ 13 m² per litre = 4 l
- Plus 10% spare = 4.4 l
- Tins: 1 × 5 l = 5 l
The rules, and their sources
Emulsion coverage per litre
Dulux says its Walls & Ceilings matt and silk emulsions cover up to 13 m² per litre on average, per coat. B&Q's and Homebase's own calculators assume 10 m² per litre.
An industry guideline Sources: B&Q, Dulux Walls & Ceilings matt emulsion 2.5 l (checked 31 October 2026); B&Q, Dulux Walls & Ceilings matt emulsion 5 l (checked 31 October 2026); Screwfix, Dulux Pure Brilliant White silk emulsion 2.5 l (checked 31 October 2026); B&Q, Wall painting calculator (checked 31 October 2026); Homebase, Paint calculator (checked 31 October 2026).
Coats of emulsion
Two coats of emulsion is the usual advice for walls and ceilings; a strong colour change can need a third.
An industry guideline Sources: Homebase, Paint calculator (checked 31 October 2026); Dulux UK, How much paint do you need? (checked 31 October 2026).
Spare paint
B&Q and Homebase advise buying about 10% more paint than the area needs, for spills, mistakes and touch-ups.
An industry guideline Sources: B&Q, Wall painting calculator (checked 31 October 2026); Homebase, Paint calculator (checked 31 October 2026).
UK emulsion tin sizes
Emulsion comes in 2.5 l and 5 l tins (some colours in 1 l). At B&Q a 5 l tin costs less per litre: £36 (£7.20/l) against £25 (£10/l) for 2.5 l of Dulux Walls & Ceilings matt.
Shop sizes Sources: B&Q, Dulux Walls & Ceilings matt 2.5 l (checked 31 October 2026); B&Q, Dulux Walls & Ceilings matt 5 l (checked 31 October 2026); Dulux UK, How much paint do you need? (checked 31 October 2026).
Other rooms
The same ceiling height, 1 door and 1 window each time. The last two rows are this size of room with more to cover.
| Walls of a room | Paint, with spare | Tins to buy |
|---|---|---|
| 3 × 3 m this page | 4.4 litres | 1 × 5 l |
| 4 × 3 m | 5.2 litres | 1 × 5 l + 1 × 2.5 l |
| 4 × 4 m | 6 litres | 1 × 5 l + 1 × 2.5 l |
| 5 × 4 m | 6.8 litres | 1 × 5 l + 1 × 2.5 l |
| 5 × 5 m | 7.6 litres | 2 × 5 l |
| 4 × 4 mwalls and ceiling | 8.7 litres | 2 × 5 l |
| 4 × 4 mnew plaster: 3 coats, the first a mist coat | 9 litres | 2 × 5 l |
Change the numbers
Your sizes will differ. The paint 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 paint 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:
- Howarth Timber (Green, 14 Sep 2026), UK door sizes, checked 31 October 2026