About Paint Calculator
Two things decide how much paint a room needs, and calculators routinely get both wrong. The first is that coverage figures are quoted per coat — a tin claiming 12 m² per litre means one coat, so painting 43 m² of wall twice is 86 m² of work and needs roughly double.
The second is the surface. Bare or new plaster drinks paint: coverage drops from about 12 m² per litre to nearer 7, and it needs a thinned mist coat first that does not count as one of your topcoats. Exterior masonry is worse again, at around 6. Using one number for every wall is how people end up short.
The result is given as tins rather than litres alone, because that is what you actually buy. Working out 4.6 litres and being handed a 2.5 and a couple of 1 litre tins is worse than simply buying one 5 litre tin, and the calculator picks the combination a sensible person would.
How to calculate paint
Measure the room
Length, width and height in metres. Wall area is worked out from the perimeter.
Subtract the openings
Enter how many doors and windows. Standard sizes are used so you do not have to measure them.
Choose surface and coats
Previously painted, bare plaster, textured, wood or masonry — each absorbs differently.