Most emulsion paints cover about 10–13 m² per litre for each coat on smooth, already-painted walls. For an average bedroom of 3.6 × 3.6 m with 2.4 m ceilings, that means roughly 5.4 litres for two coats on the walls, so three 2.5 litre tins, or a 5 litre tin plus a 1 litre tin.
This guide shows how to measure a room, how to turn square metres into litres, how much extra to allow for new plaster and colour changes, and a quick table for common room sizes. If you would rather skip the sums, the paint calculator does it for any room.
Quick guide: paint for common room sizes
These figures assume 2.4 m high walls, one door, two windows, two coats and a coverage of 11 m² per litre, which is typical for a standard matt or silk emulsion. Ceilings are listed separately because they are often painted in a different colour or product.
| Room (floor size) | Wall area to paint | Walls, 2 coats | Ceiling, 2 coats |
|---|---|---|---|
| Small bedroom (3 × 3 m) | 24 m² | 4.4 litres | 1.6 litres |
| Average bedroom (3.6 × 3.6 m) | 30 m² | 5.4 litres | 2.4 litres |
| Double bedroom (4 × 3.5 m) | 31 m² | 5.7 litres | 2.5 litres |
| Living room (4.5 × 4 m) | 36 m² | 6.6 litres | 3.3 litres |
| Large living room (5 × 4 m) | 38.5 m² | 7.0 litres | 3.6 litres |
Always check the coverage printed on your tin. Cheaper paints often cover less, and some one-coat or high-opacity products claim more.
Step 1: measure the walls
You only need three measurements: the length and width of the room, and the height from the floor to the ceiling.
- Add up the length of all four walls. For a 3.6 × 3.6 m room that is 3.6 + 3.6 + 3.6 + 3.6 = 14.4 m. For a rectangular room, it is 2 × (length + width).
- Multiply by the wall height. 14.4 × 2.4 = 34.6 m² of wall.
- Take off doors and windows. A standard internal door is about 1.9 m² and an average window about 1.4 m². With one door and two windows, that is 34.6 − 1.9 − 2.8 = 29.9 m² to paint.
If your windows are very large, such as patio doors or a bay, measure them properly and subtract the real area. For small windows, many decorators do not bother subtracting them, which gives a little built-in spare.
Step 2: turn square metres into litres
The formula is simple:
Litres = wall area × number of coats ÷ coverage per litre
For the example room: 29.9 m² × 2 coats ÷ 11 m² per litre = 5.4 litres.
Paint is sold in fixed tin sizes, so the last step is choosing tins. In the UK, emulsion usually comes in 1, 2.5, 5 and 10 litre tins. For 5.4 litres you could buy three 2.5 litre tins (7.5 litres) or one 5 litre tin and one 1 litre tin (6 litres). The second option leaves less waste and is often cheaper per litre. In Australia, 4 litre and 10 litre cans are more common, so a single 4 litre can plus a 2 litre can would do the same room.
Do you really need two coats?
Almost always, yes. One coat can look fine when it is wet, but it usually dries patchy, especially on the edges you cut in with a brush. Two coats give an even colour and a finish that lasts. Plan for more in these situations:
- Big colour changes. Going from a dark colour to a light one, or light to a strong red or yellow, often needs a third coat. A tinted primer or undercoat can save a coat of your more expensive top coat.
- New plaster. Fresh plaster is thirsty and soaks paint in. Seal it first with a mist coat: a first coat of matt emulsion thinned with water, following the tin or plaster manufacturer’s guidance. Allow roughly an extra coat’s worth of paint for it.
- Rough or textured walls. Artex, bare brick and heavily textured surfaces can use 20–30% more paint than smooth walls because there is simply more surface.
Ceilings, woodwork and extras
Measure the ceiling as length × width. The 3.6 × 3.6 m bedroom has a 13 m² ceiling, so two coats at 11 m² per litre need about 2.4 litres: one 2.5 litre tin of ceiling or matt white.
Skirting boards, door frames and windows need a separate trim paint such as satinwood or gloss. These go much further, because the surface area is small: a 750 ml tin usually does the woodwork in an average room, with two coats.
Do not forget the kit. For a typical room you will need a roller and tray, a 2 inch brush for cutting in, masking tape, dust sheets, filler and sandpaper for repairs, and a sugar soap solution to clean the walls first.
If you measure in feet and gallons
In the US, a gallon of interior paint typically covers 350–400 sq ft per coat. A 12 × 12 ft room with 8 ft walls has 384 sq ft of wall; minus one door (about 21 sq ft) and two windows (about 15 sq ft each) that leaves 333 sq ft. Two coats at 350 sq ft per gallon need 1.9 gallons, so two 1-gallon cans. Switch the paint calculator to USA to work in feet and gallons.
Tips to avoid running short (or wasting a tin)
- Buy everything at once. Colours can vary slightly between batches. If you need more than one tin, pour them into a larger bucket and mix them together, a trick called boxing.
- Keep a little back. A small amount of leftover paint is handy for touch-ups. Label the tin with the room and date.
- Check the coverage, not just the price. A cheaper paint that needs three coats can cost more than a better one that covers in two.
- Write down your measurements. It makes it easy to recalculate if you change colour or product in the shop.
Frequently asked questions
How many square metres does 1 litre of paint cover?
Usually 10–13 m² per coat on a smooth, previously painted wall. That drops on new plaster or rough surfaces. For two coats, 1 litre covers roughly 5–6 m² of wall.
Is 5 litres of paint enough for a bedroom?
For an average bedroom of around 3.6 × 3.6 m, 5 litres is just short for two coats on the walls, which need about 5.4 litres. A small bedroom of 3 × 3 m needs about 4.4 litres, so 5 litres is enough.
How much paint do I need for a ceiling?
Multiply the ceiling length by the width, double it for two coats and divide by the coverage. A 4 × 3.5 m ceiling is 14 m², so about 2.5 litres for two coats.
Does darker paint need more coats?
Strong, dark colours often need three coats for an even finish, especially over a lighter base. Some manufacturers recommend a coloured base coat first. Check the tin.
Work out your own room: the free paint calculator takes off doors and windows and tells you how many tins to buy. Papering one wall instead? Try the wallpaper calculator.
Figures are estimates for planning. Coverage varies by product and surface, so check the tin before you buy.
Related: the DIY Project Budget & Materials Planner turns your measurements into quantities, costs and a shopping list.
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