Paint calculator

A 4 × 3.5 m room with 2.4 m ceilings, a door and a window has about 32.9 m² of wall. Two coats at 12 m² a litre is about 5.5 litres: a 5 L and a 2.5 L tin.

Two for most walls, the same colour or a similar one. Three over a strong or dark colour, and a mist coat first on new plaster.

The square metres one litre covers in one coat, on a smooth, sound surface. Emulsion is often 10 to 14 m² a litre. Rough or porous surfaces, like bare plaster, render or brick, take more paint: lower the figure.

A UK (imperial) gallon is 4.546 litres; a US gallon is 3.785 litres. Paint in the UK and Ireland is sold in litres, so the calculator works in litres and shows both gallons too.

Tick it if the ceiling takes the same paint as the walls. Ceilings are often a different white: then work the walls out first, and the ceiling separately with the area option (length × width of the room).