Paint Calculator for a Room
Works out wall paint for a room from its length, width and height. Doors and windows are deducted at typical sizes, and the ceiling can be added.
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The formula
litres = area ÷ coverage per litre × coats
Coverage is the whole calculation, and it is the figure tins are most optimistic about. The label quotes a smooth, sealed, previously painted surface; bare plaster, textured render and a strong colour change all take noticeably more.
What to watch out for
The wall area is the perimeter times the height, less the openings:
- Perimeter, not floor area. A 4 × 3.5 m room has a 15 m perimeter, so at 2.4 m high that is 36 m² of wall before deductions — far more than the 14 m² of floor.
- Doors and windows come off. About 1.8 m² for a standard door and 1.5 m² for a window. Precision is not needed; the waste in a tin is larger than the error.
- The ceiling is separate if the colour differs. Most ceilings are white and most walls are not, which means two tins and two coverage figures.
Frequently Asked Questions
How much paint for a 4 × 3.5 m room?
With 2.4 m walls, one door and two windows, that is about 31 m² of wall — roughly 5.7 litres for two coats. Two 2.5 L tins plus a 1 L, or a single 5 L and a 1 L.
How do I calculate the wall area of a room?
Add the lengths of all four walls to get the perimeter, multiply by the height, then subtract about 1.8 m² per door and 1.5 m² per window.
Should I include the ceiling in the same tin?
Only if it is the same colour and finish. Ceilings normally take a dedicated matt white, and ceiling paint is formulated to drip less — which matters more than the price difference.