How paint quantity is estimated
The paint you need is the area to cover, multiplied by the number of coats, divided by the coverage of your paint. Coverage — how many square metres one litre covers — varies by product and surface, typically 10–14 m² per litre for smooth interior walls and less for rough or porous surfaces. Because it's editable here, you can match the exact figure printed on your paint tin.
Measuring the area
For a room, add up the length of every wall, multiply by the ceiling height, then subtract large openings like doors and windows. New drywall, bare plaster and strong colour changes usually need an extra coat, which is why the coats field matters as much as the area.
Buying the right amount
It's wise to buy slightly more than the estimate so you have enough for touch-ups and don't risk a batch-colour mismatch later. Paint is sold in fixed tin sizes, so round up to the next tin — the result here tells you the minimum litres, not the nearest can.
Frequently asked questions
What coverage should I use if I don't know it?
10 m² per litre is a safe default for a single coat on smooth interior walls. Check your tin's label for the exact figure and enter it for a more precise estimate.
How many coats do I need?
Two is standard for good coverage. One may be enough when repainting a similar colour; three can be needed over bare surfaces or when going from dark to light.