The short answer
A 3.5 × 3 m bedroom with 2.4 m walls, one door and one window needs about 6.5 litres of wall paint for two coats at 10 m² per litre with 10% extra. The ceiling needs about 2.5 litres of ceiling paint on top. Use the coverage printed on your tin rather than 10 m² per litre, and use the paint calculator to try your own figures.
Try the Paint CalculatorMeasure the walls
Measure the length and width of the room and the height of the walls. The wall area is the perimeter (2 × length + 2 × width) multiplied by the height. Take off the doors and windows: about 1.9 m² for a standard door and 1.5 m² for an average window are sensible allowances.
For a 3.5 × 3 m room with 2.4 m walls, the perimeter is 13 m, so the gross wall area is 13 × 2.4 = 31.2 m². With one door and one window taken off (3.4 m²), the paintable area is 27.8 m².
Choose the number of coats and the coverage
Two coats is a sensible default for a colour change. Allow a third coat or a primer for dark colours, a big change from dark to light, or bare plaster. The coverage on the tin, in square metres per litre, is the figure to use. A cautious 10 m² per litre is the calculator's default if you do not know it.
For two coats at 10 m² per litre, 27.8 m² needs 27.8 × 2 ÷ 10 = 5.56 litres. Add 10% for losses in the tray, roller and cutting in: 6.12 litres. Rounded up to the next half litre, that is 6.5 litres.
Add the ceiling, woodwork and primer
The ceiling area is the length times the width: 3.5 × 3 = 10.5 m². Two coats at 10 m² per litre needs 2.1 litres, or about 2.3 litres with 10% extra, so 2.5 litres. Ceiling paint often has a different coverage, so use the figure on the tin.
Skirting boards, window frames and doors use a different paint, usually satin or gloss, and a small tin is normally enough for a single room. A primer or mist coat is needed on bare plaster and may be needed over stains.
Turn the litres into tins
Emulsion is commonly sold in tins of 2.5 litres, 5 litres and 10 litres, although sizes vary by brand. For 6.5 litres, a 5 litre tin plus a 2.5 litre tin gives 7.5 litres, which leaves a little for touch-ups.
Buy all the tins at once, from the same batch if possible, and mix them together in a large bucket before you start to avoid a colour difference between tins. Keep the leftovers for touch-ups, labelled with the room and the date.
- Walls: 6.5 litres for two coats.
- Ceiling: 2.5 litres for two coats.
- Woodwork and primer: check the product, as the amounts are small.
This guide is general information to help you plan, not professional advice. Check product instructions and your supplier's guidance before you buy, and ask a qualified professional about structural or safety-related work. See our terms of use.