Paint Calculator

Paint coverage is quoted for a sealed, even, light-coloured surface: 12 to 14 m² per litre for emulsion on a properly primed wall, 10 to 12 for a scrubbable finish, 8 for a porous or heavily textured surface. A newly plastered wall absorbs far more, and the first coat can disappear at 60 % of the stated coverage.

Two coats are normal, and the second covers less area per litre than the first because the surface is already sealed. Multiplying the tin's number by the wall area and calling it done underestimates a real job by a third.

Primer is not optional on new plaster or on a patch repair, and it is cheaper than the paint it saves. Going from a dark colour to a light one often needs three coats over a primer, which is a different quantity, not the same quantity applied twice.

Roller pile matters as well: a short pile on a smooth wall wastes little, a long pile on brickwork or render wastes a lot and is unavoidable. The same square metre can take 0.12 litres or 0.3 litres depending on the surface, so the calculator asks for the surface and expects an honest answer.

Ceilings are usually painted a different colour in a different finish, so they are a separate line even when the area is small. Doors, frames and skirting take 10 to 15 % on top of the wall area in a normal room and are the reason a job that looked like four litres needs five.

Buy in the largest tin that matches your job: two 5 litre tins of the same batch are consistent, two 2.5 litre tins of different batches may not be, and leftover paint from the same batch is what makes a future repair invisible.