How this calculator works
The paintable area is the four walls (the perimeter × the ceiling height) minus the doors and windows. Multiply by the number of coats and divide by how many square metres a litre covers, usually about 12 for emulsion. The ceiling is length × width, worked out the same way.
Worked example: a 4 × 3 m room with a 2.4 m ceiling has 33.6 m² of wall. One door and one window take off 3.1 m², leaving 30.5 m². Two coats at 12 m² per litre is 30.5 × 2 ÷ 12 = 5.1 litres, so buy a 5 litre tin and a 1 litre tin, or one 5 L and one 2.5 L. The 12 m² ceiling needs another 2 litres.
Tips before you buy
- New plaster needs a mist coat first: a watered-down coat of emulsion (about 70% paint to 30% water) that soaks in and seals it. Then apply your two full coats.
- Fill and sand cracks and holes, and wash greasy areas, before painting. Paint will not hide poor preparation.
- Use a contract matt (flat) emulsion on ceilings, which hides flaws, and a wipeable matt or silk on walls in kitchens and bathrooms.
- Buy all the paint for a room together and mix the tins into one container, so the colour is identical on every wall.
- Rough walls and dark colours cover less. Use the lower coverage figure, and consider a primer or a tinted undercoat for big colour changes.
- Houses built before about 1960 may have lead-based paint. Test before sanding or scraping, and do not dry-sand old paint.
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?
About 5 litres for the walls with two coats, if the room is 2.4 m high with one door and one window, and another 2 litres for the ceiling.
How much does a litre of emulsion cover?
About 12 m² per coat on smooth, previously painted walls. The tin states its coverage, and bare plaster, rough walls and dark colours cover less.
What size tins does paint come in?
Most emulsion is sold in 1 litre, 2.5 litre, 5 litre and 10 litre tins, and larger tins are cheaper per litre.
Do I need two coats of paint?
Almost always. Two coats give an even finish and good coverage. Use a mist coat first on new plaster.
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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.