Our paint calculator tells you how many litres of paint you need to cover a room, taking into account the wall area, ceiling area, and any doors or windows you want to exclude. You can also specify the number of coats — most surfaces need two coats for good coverage. The calculator uses a standard coverage rate of 10–12 square metres per litre for emulsion paint, which is typical for most interior wall paints. Coverage rates vary by paint type and surface texture, so always check the manufacturer's guidance on the tin. It is always worth buying slightly more than calculated to ensure you have enough for touch-ups.