How much paint do I need for a room?
Work out the wall area, take off the doors and windows, then multiply by the number of coats and divide by the coverage on the tin. A 4 × 3 m room with 2.4 m walls, one door and one window has 30.68 m² of wall: two coats at 12 m² a litre, plus 10% waste, comes to 5.62 litres.
Measuring
Measure the length of each wall and the height from the floor to the ceiling, in metres. For a plain rectangular room you only need the room's length, width and height: the walls are the perimeter times the height.
- 4 m + 3 m + 4 m + 3 m = 14 m of wall
- 14 m × 2.4 m = 33.6 m²
For the ceiling, multiply the room's length by its width: 4 × 3 m = 12 m². Measure alcoves, chimney breasts and sloping ceilings as separate rectangles and add them up. The paint calculator takes a whole room, separate walls or a ceiling.
Doors and windows
Take off anything you're not painting. Multiply each door's and window's width by its height:
- door, 0.8 × 2 m = 1.6 m²
- window, 1.2 × 1.1 m = 1.32 m²
- 33.6 − 1.6 − 1.32 = 30.68 m² to paint
Small openings make little difference, so if you're unsure, leave them in: you'll have a little spare rather than run short.
Coats and real coverage
Coverage is the area one litre covers in one coat, and it's printed on the tin. The calculator starts from 12 m² a litre and two coats, and you can change both to match your paint. For the walls above:
- 30.68 m² × 2 coats = 61.36 m² of painting
- 61.36 ÷ 12 m² a litre = 5.11 litres
- plus 10% waste = 5.62 litres
The tin's figure is a best case on a smooth, sealed surface. Fresh plaster, rough or patched walls and a big change of colour all use more, and may need an extra coat. New plaster needs a thinned mist coat first: see painting new plaster, and use the mist coat setting in the calculator.
For woodwork such as skirting, door frames and doors, multiply the length by the height or width to get the area in m², and use the coverage on the tin of gloss, satin or eggshell you're buying: it's usually different from wall paint.
Tins and leftovers
Paint comes in fixed tin sizes, so the calculator finds the mix of tins with the least left over. Starting from 1, 2.5, 5 and 10 litre tins:
- walls, 5.62 litres: one 5 litre tin and one 1 litre tin (6 litres, 0.38 litres spare)
- ceiling, 12 m² at two coats: 2.2 litres, so one 2.5 litre tin (0.3 litres spare)
Change the tin sizes in the calculator to the sizes your paint comes in. A little spare is useful for touching up later: keep the lid on tight and note the colour name on the tin.
FAQs
How many m² does a litre of paint cover?
It depends on the paint and the surface, so check the tin. The calculator starts from 12 m² a litre per coat for walls and ceilings and lets you change it. Rough, porous or freshly plastered walls use more than the tin says.
Do I need two coats of paint?
Usually, yes, for an even finish, and the calculator assumes two. A light colour over a similar one may cover in one; a big colour change or new plaster may need three. Change the number of coats in the calculator to see the difference.
Should I take off doors and windows?
Yes, if they're large or there are several of them. For a room with one door and one window, it makes a small difference: in the example above, 2.92 m² out of 33.6 m².
How much paint for a ceiling?
Multiply the room's length by its width for the area. A 4 × 3 m ceiling is 12 m²; two coats at 12 m² a litre plus 10% waste is 2.2 litres, so one 2.5 litre tin.
Is it cheaper to buy one big tin or several small ones?
The calculator doesn't use prices. It shows the mix of tins with the least left over and the mix with the fewest tins, so you can compare them against your supplier's prices yourself.