How Many Litres of Paint Do I Need for a Room?
A simple way to calculate how much paint you need for walls, ceilings and woodwork, with coverage guidance, allowances for coats and common over-buying mistakes.
Buying too little paint means a second trip and a risk of colour mismatch. Buying too much wastes money. A quick calculation gets you close, and a few rules of thumb deal with the details.
Step 1: Measure the wall area
Measure the length of each wall and the height from floor to ceiling. Multiply length by height for each wall, then add them up.
For example, a room with two walls of 4 m and two of 3 m, at a height of 2.4 m:
- Perimeter: 4 + 4 + 3 + 3 = 14 m
- Wall area: 14 x 2.4 = about 33.6 square metres
Step 2: Subtract openings
Subtract the area of large windows and doors. As a loose guide, a standard door is around 1.6 square metres and a typical window may be 1 to 2 square metres. If you are being cautious, you can leave smaller openings in, which gives a little extra paint.
Step 3: Check the coverage on the tin
Coverage is printed on the tin and is usually given in square metres per litre for one coat on a smooth, sealed surface. Many emulsions cover somewhere around 10 to 14 square metres per litre, but this varies by product, and the number is a guide rather than a guarantee.
Divide your area by the coverage figure to get litres per coat, then multiply by the number of coats.
For the example above, at about 12 square metres per litre:
- 33.6 / 12 = about 2.8 litres per coat
- Two coats = about 5.6 litres
In practice, that suggests one 5-litre tin plus a smaller 2.5-litre tin, or a 7.5-litre option.
Adjustments that change the amount
Surface porosity
Bare plaster, filler, lining paper and previously unpainted surfaces soak up paint. Apply a mist coat or sealer first. See mist coating new plaster.
Colour change
Covering a dark colour with a pale one, or a strong colour with a lighter shade, can need extra coats. Rich reds, deep blues and some yellows often need more coats than neutrals.
Texture
Textured walls, woodchip and Artex use more paint than smooth plaster.
Ceilings
Calculate ceiling area as length x width, then use the same coverage method. Dedicated ceiling paint is often thicker, which helps with spatter.
Woodwork
Gloss, satin and eggshell cover a smaller area per litre than emulsion, often something like 12 to 16 square metres per litre but check the tin. A typical room's woodwork may only need a 750 ml to 1 litre tin. Priming and undercoating add to this if the old finish is worn or you are changing colour dramatically.
Quick rule-of-thumb table
| Room | Typical emulsion for walls, two coats |
|---|---|
| Small bathroom | 2 to 2.5 litres |
| Average bedroom | 4 to 5 litres |
| Living room | 5 to 7.5 litres |
| Hallway and landing | 5 to 7.5 litres |
These are only starting points. Always measure your own room.
Tips to avoid waste
- Buy slightly more than you need if you are matching a custom colour, because mixing again may vary a little.
- Keep the leftover paint in a sealed tin, labelled with the room and date.
- Combine tins of the same batch in a bucket to even out minor variation.
- Check whether your decorator will supply paint, to avoid duplicates. See should you buy paint yourself.
A worked example: a bedroom with two windows and a door
A bedroom is 4 m by 3.5 m with 2.4 m ceilings. The perimeter is 15 m, so wall area is 15 x 2.4 = 36 square metres. Take off about 2 square metres for the door and 3 for two windows, leaving 31 square metres. Two coats means 62 square metres to cover. If the tin says 12 square metres per litre, that is a little over 5 litres, so one 5 litre tin plus a small tester or a second tin gives comfortable margin. The ceiling, 14 square metres, needs two coats of 28 square metres, so roughly 2.5 litres of ceiling paint.
Quick formula
- Perimeter x ceiling height = total wall area
- Subtract doors and windows
- Multiply by number of coats
- Divide by the coverage figure on the tin (square metres per litre)
- Add around 10 per cent for waste and touch-ups
Coverage varies
| Surface | Effect |
|---|---|
| New plaster or bare surface | Absorbs a lot, usually needs a mist coat first |
| Previously painted and sealed | Closer to the stated coverage |
| Rough or textured | Uses more paint |
| Dark to light change | Needs an extra coat |
Common mistakes
- Using the tin's coverage figure for one coat when you need two. Many people forget to double.
- Forgetting the ceiling and woodwork. They use different products.
- Not allowing for cutting in and tray waste. A small margin avoids running out.
- Buying tins of custom colour at different times. Batches can differ slightly.
Edge cases
Feature walls. A single dark wall may need three coats, so allow for it.
Stairwells. Measure each wall surface separately; sloping walls follow the stair line, so use average height.
Rental or touch-up. Keep a labelled, sealed tin with colour name and finish for repairs.
Checking before you buy
Measure twice, check the coverage figure for the specific paint, and ask a decorator or the paint supplier if you are in doubt. Custom-tinted colours are made to order, so be sure of the quantity before you commit to large volumes. If a decorator is supplying paint, agree the quantity and any leftover arrangements before they start.
Frequently asked questions
Do I need to subtract windows and doors?
Doing so gives a more accurate figure, but it is often safer to leave small openings in as a buffer. For large glazed doors or patio doors, subtract them.
How much paint do I need for a ceiling?
Measure length by width, then divide by the coverage on the tin. Most ceilings need two coats, so double the amount.
Is it better to buy one big tin or several small ones?
One large tin gives consistent colour. If you buy several, mix them together in a bucket before use so slight variations even out.