Paint Calculator
Litres or gallons and tins for a room from its size, openings and coats.
About this tool
Enter the room's length, width and wall height, the number of doors and windows, coats, the coverage figure from your paint tin and the tin size. The tool returns the area to paint, the paint needed and the number of tins, in metric or imperial. Tick the ceiling to include it.
Getting the amount right
The sum is simple โ wall area minus openings, times coats, divided by coverage โ and the mistakes are all in the inputs. Coverage varies more than people expect: a good emulsion covers 10โ14 mยฒ per litre on smooth plaster, but bare new plaster, textured surfaces and a dark-to-light change can halve that, and primer covers less than topcoat. Two coats is standard; a third is common over a strong colour. The tool subtracts standard openings (1.6 mยฒ per door, 1.4 mยฒ per window) and rounds up to whole tins, and the sensible habit is to buy about 10% more than the total for touch-ups from the same batch, because batches differ slightly in shade. Odd-shaped rooms: add up the wall lengths and enter half as length and half as width. The tile calculator does the same job for tiling, the area calculator handles unusual shapes, and the unit converter moves between metres and feet.
Frequently asked questions
How much does one litre of paint cover?
Typically 10โ14 mยฒ for emulsion on smooth walls (350โ400 sq ft per US gallon). Use the figure on your tin โ it accounts for that paint's formulation.
Do I need to subtract doors and windows?
Yes for accuracy; the tool uses standard sizes. Ignore it for a small window and you simply buy a little extra, which is not a bad outcome.
How many coats?
Two for most walls. One over a similar colour with a quality paint; three (or a mist coat) over new plaster or a dark colour.
Does it include ceilings and trim?
The ceiling if you tick it. Trim (skirting, doors, frames) uses a different paint โ estimate that separately by running length.