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How much paint do I need?
To paint a room you first work out the wall area (the distance around the room times the wall height), subtract the doors and windows you won’t be painting, then multiply by the number of coats. One US gallon of interior paint typically covers about 350 square feet per coat. This calculator does all of that and tells you how many gallons (and litres) to buy — plus a little extra for touch-ups.
Buying the right amount matters: run short mid-job and the new can may not match; buy far too much and you’ve wasted money. This gets you close.
Estimate based on ~350 sq ft coverage per gallon per coat. Rough, textured or unpainted (bare/primer) walls soak up more — round up, and keep a little spare for touch-ups.
Frequently Asked Questions
How many gallons of paint for a 12×12 room?
A standard 12×12 room with 8-ft walls needs roughly 2 gallons for two coats (about 1 gallon per coat after subtracting a door and window). Enter your exact size above for a precise number.
Does the calculator include primer?
No — primer is separate. If your walls are bare, patched, or you’re painting a light colour over a dark one, add one coat of primer (primer covers a similar area, ~200–300 sq ft per gallon).
How many coats do I need?
Two coats is standard for an even finish and true colour. Use three when going light over dark, and one only when refreshing the same colour on a good surface.
Should I paint the ceiling too?
Tick the ceiling box above and the calculator adds the ceiling area (length × width). Ceilings often need their own flat ceiling paint rather than wall paint.