About this calculator
How much paint a room needs, split into wall and ceiling paint, with sensible tin sizes so you don’t overbuy.
How it’s calculated
Paint = area × coats ÷ coverage. Typical coverage is 10–14 m² per litre for emulsion on smooth plaster. Doors and windows are deducted at standard sizes.
Worked example
With these inputs:
- Room length
- 4.2 m
- Room width
- 3.6 m
- Wall height
- 2.4 m
- Doors
- 1
- Windows
- 2
- Paint the ceiling
- Yes
- Coats
- 2
- Coverage (m² per litre)
- 12
- Add a primer / mist coat
- No
the result is:
- Wall paint
- 5.4 L
- Wall area (net)
- 32.54 m²
- Ceiling area
- 15.12 m²
- Primer
- 0 L
Tips from the trade
- New plaster or drywall is thirsty: prime or mist-coat it first.
- Rough, textured or dark surfaces can drop coverage by 20–30%.
- Big colour changes (dark to light) usually need a third coat.
Common questions
How much paint for a 12×12 room?
With 2.4 m walls and two coats, about 7 litres for the walls and 3 for the ceiling.
Results are estimates for planning and pricing. Check quantities against your drawings, the manufacturer’s data and the Building Regulations before ordering.