Paint calculator
Enter the room size in metres and count the doors and windows. The calculator takes them off the wall area for you.
Measuring in feet and inches? Use the US version
Paint needed
5.6 litres
- Tins to buy
- 3 2.5 litre tins
- Paintable area
- 33.5 m² per coat
How it works
Wall area is the room’s perimeter (2 × length + 2 × width) times the wall height. The calculator takes off about 1.9 m² per door and 1.5 m² per window, adds the ceiling if you’re painting it, multiplies by the number of coats and divides by the coverage on the tin.
Coverage on the tin assumes smooth, sealed walls. Fresh plaster, bare wood and textured walls soak up more, so use a mist coat or primer first.
Example
With room length 4 m, room width 4 m, wall height 2.4 m, doors 1, windows 2, coats 2, coverage 12 m² per litre, tin size: 2.5 litre, paint the ceiling too: no, walls only, the answer is 5.6 litres.
Tips before you buy
- New plaster needs a thinned mist coat or primer before the finish coats.
- Changing to a very different colour usually takes two coats, sometimes three for strong colours.
- Keep a little leftover paint, labelled with the room and colour, for touch-ups.
Common questions
How much paint do I need for a 4 × 4 m room?
With 2.4 m walls, one door and two windows, about 5.6 litres for two coats on the walls, which is three 2.5 litre tins.
How many square metres does a litre of paint cover?
Most wall paints list 10–14 m² per litre for one coat on a smooth, sealed surface.
Do I need two coats of paint?
Usually, yes. Two coats give even colour and a more durable finish.