Paint Calculator: How Much Paint Do I Need for a Room?

Buying too much paint wastes money; buying too little means a second trip and a possible batch mismatch. This calculator works out the litres, tins and cost from your wall area, your number of coats, and the doors and windows you will not be painting. The key number most people miss is spreading rate: a litre of emulsion covers far less than the tin suggests once you account for two coats.

We deduct 1.8 m² per door and 1.5 m² per window, then round each coat up to whole tins. Primer on bare plaster or a dark-to-light change will need an extra coat. If the room has feature walls in a second colour, run the calculator once per colour.