Paint Calculator
Work out how much paint you need for a room's walls or ceiling, allowing for doors, windows and the number of coats, with tin sizes to buy.
New: please check your results.
- Paint needed
- 5 litres
- In UK tin sizes
- 1 × 5 L + 1 × 1 L
- Area to paint (one coat)
- 30.2 m²
What it does
Find how many litres of paint a room needs. Enter its size, how many doors and windows there are and how many coats you'll apply, and see the area to cover, the paint needed and the tins to buy. It works for walls, a ceiling, or both.
How to use it
- What are you painting?
Ceilings usually take a different paint from walls, so work them out separately if you're buying different tins.
- Room length
The length of the room, wall to wall.
- Room width
The width of the room, wall to wall.
- Wall height
Floor to ceiling. Most UK rooms are about 2.4 m (8 ft).
- Doors
Each door takes off about 1.9 m² (20 ft²), frame included.
- Windows
Each typical window takes off about 1.5 m² (16 ft²). Count a large patio door as a door plus a window.
- Coats
Two coats is normal. A new plaster mist coat, a big colour change or covering a dark colour can need three.
- Paint coverage
How far one litre goes, printed on the tin: emulsion is usually 10 to 14 m² per litre. Use a lower number for rough or new plaster.
Common uses
- Buying the right amount of emulsion before decorating.
- Comparing the cost of different paints by coverage.
- Working out tiles for a kitchen or bathroom wall. Try the Tile Calculator
- Working out the area of an awkward shape. Try the Area Calculator
The formula
Wall area = 2 × (length + width) × height − doors − windowsCeiling area = length × widthPaint (litres) = area × coats ÷ coverageWhere:
- Door
- about 1.9 m² each, frame included
- Window
- about 1.5 m² each
- Coverage
- square metres one litre covers, from the tin
Tins are suggested from the common 5 L, 2.5 L and 1 L sizes. Buy a little extra if the paint is a mixed colour, so a second batch doesn't have to match.
Worked example
A room 4 m by 3 m with 2.4 m walls, 1 door and 1 window:
- Walls: 2 × (4 m + 3 m) × 2.4 m = 33.6 m²
- Less the door and window: 33.6 − 3.4 = 30.2 m²
- Paint: 30.2 m² × 2 coats ÷ 12 m² per litre = 5 litres
Tins: 1 × 5 L + 1 × 1 L.
Questions people ask
How much paint do I need for an average room?
A 4 m by 3 m bedroom with 2.4 m walls, one door and one window has about 30 m² of wall. Two coats at 12 m² per litre need about 5 litres, so one 5-litre tin.
Do I need two coats?
Usually, yes. One coat rarely gives an even finish, especially with a colour change. New plaster needs a thinned 'mist coat' first, so allow three.
Should I allow for wastage?
The result is the paint you'll actually put on. Rollers and trays hold some, and rough walls drink more, so rounding up to the next tin size is sensible, as the tin suggestion does.
Last checked 26 October 2026