Paint calculator
How much paint you need for a room, and which tin sizes to buy.
How it works
Wall area is the room's perimeter × wall height, minus a standard allowance for each door (about 21 sq ft or 1.9 m²) and window (about 15 sq ft or 1.4 m²). We multiply by the number of coats and divide by the coverage on the tin. Then we pick the mix of tin sizes that costs least, since paint is cheaper per litre in larger tins.
Coverage varies more than you think
US labels often say 350–400 sq ft per gallon; metric labels range from about 10 to 16 m² per litre. Rough, textured or porous surfaces such as new plaster, bare wood and masonry soak up more. We start at 350 sq ft per gallon or 10 m² per litre, toward the low end, so you are less likely to run short.
Tips before you buy
- New plaster or plasterboard (drywall in the US and Canada) usually needs a mist coat or primer first.
- Going from dark to light often takes an extra coat. A tinted primer can save one.
- Buy all your tins of a colour at once. Mixing batches can show slight colour differences.
Common questions
How much paint do I need for a 12 × 12 ft room?
With 8 ft walls, one door, two windows and two coats at 350 sq ft per gallon, about 1.9 gallons. That means buying two gallons.
Do I include the ceiling?
Only if you are painting it the same paint. Ceilings usually get a dedicated ceiling paint, so many people calculate them separately.
Reviewed by Alex Rowan, Editor. Last reviewed . How we calculate · Report a problem