Paint Coverage by Coats Calculator

How it is calculated

Enter the wall area in m², the number of coats and the spread rate in m² per litre per coat, as printed on the tin. The tool computes total area = area × coats and litres = total area / spread rate. It also shows litres with waste = litres × 1.1, a fixed 10 % allowance for spills, brush and roller loss and uneven surfaces. The number of coats must be at least 1. Openings such as doors and windows are not subtracted, so deduct them from the area yourself. The spread rate on the tin assumes a smooth, previously painted surface; bare plaster or rough walls absorb more paint and need a lower spread rate.

Common mistakes

• Entering the spread rate for the whole job instead of per coat: tins state coverage per coat, and the tool multiplies by the coats itself.
• Forgetting to subtract large windows and doors, or forgetting the ceiling, so the area is not the real surface to paint.
• Using the tin's best-case spread rate on bare plaster or a porous wall, which soaks up more paint, so enter a lower figure.
• Entering the floor area of the room instead of the wall area: wall area is roughly perimeter times ceiling height.
• Fractions of a coat such as 2.5: the tool accepts them, but a real job has whole coats, so round to what you will actually apply.