How this calculator works
This runs our paint calculator, and the skirting calculator if you are replacing the skirting. The walls are the perimeter times the ceiling height less the doors and windows; the ceiling is length times width; each is multiplied by the number of coats and divided by the coverage per litre.
Worked example: a 4 × 3 m room with a 2.4 m ceiling, one door and one window needs 5.1 litres for the walls with two coats at 12 m² per litre, 2.0 litres for the ceiling, and 38 m of masking tape. Together that is 7.1 litres.
Assumptions and sources
- New plaster needs a mist coat first: emulsion thinned with about 30% water so that it soaks in and seals the surface. Then paint two full coats. Houses built before about 1960 can have lead-based paint: test before sanding, and do not dry-sand old paint. The tin states its own coverage, which wins over ours.
The formula and a worked example are shown above, so you can check any result by hand. Read how we calculate and check our numbers. Results are estimates for planning: supplier products vary, so check the size printed on the label.
Paint by room size (2.4 m ceilings, 1 door, 1 window, 2 coats, 12 m² per litre)
Litres for the walls and for the ceiling.
| Room | Walls | Ceiling | Together |
|---|---|---|---|
| 3 × 3 m | 4.3 L | 1.5 L | 5.8 L |
| 3.5 × 3 m | 4.7 L | 1.8 L | 6.4 L |
| 4 × 3 m | 5.1 L | 2.0 L | 7.1 L |
| 4 × 4 m | 5.9 L | 2.7 L | 8.5 L |
| 5 × 4 m | 6.7 L | 3.3 L | 10.0 L |
| 5 × 5 m | 7.5 L | 4.2 L | 11.7 L |
Tips before you buy
- Buy all the paint for a room at once and mix the tins into one container, so the colour is the same on every wall.
- Fill and sand cracks and holes, and wash greasy areas, before painting. Paint will not hide poor preparation.
- Use a contract matt on ceilings and a wipeable matt or silk on walls in kitchens and bathrooms.
- Rough walls and dark colours cover less. Use the lower coverage figure.
- Keep a little paint in a small, full, sealed pot for touching up.
Tools & materials for this project
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Frequently asked questions
How many litres of paint do I need for a 4m x 3m room?
5.1 litres for the walls with two coats, if the room is 2.4 m high with one door and one window, and 2.0 litres for the ceiling. That is 7.1 litres in all.
How much does a litre of emulsion cover?
About 12 m² per coat on smooth, previously painted walls, and as little as 10 m² on rough or bare plaster. The tin states its coverage.
What size tins does paint come in?
Most emulsion is sold in 1 litre, 2.5 litre, 5 litre and 10 litre tins. Larger tins cost less per litre, so buy one big tin rather than several small ones.
How much paint is needed for just the walls?
5.1 litres for two coats. The ceiling adds 2.0 litres.
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Related calculators & guides
Estimates only. Results assume standard materials and simple shapes. Supplier products vary, and the final call on quantity, structure and safety is yours. Check your local code and your supplier's guidance before ordering.