Paint Calculator
Work out how much paint you need for a room, minus doors and windows.
Coverage varies by paint and surface. Porous, rough or freshly plastered walls and strong colour changes can need noticeably more paint — check the label on your tin.
About this tool
Enter the total length of the walls, the wall height, the number of doors and windows and how many coats you plan. The calculator subtracts standard door and window sizes and tells you how many litres or gallons of paint to buy.
Frequently asked questions
Multiply the total wall length by the wall height, subtract doors and windows, then multiply by the number of coats and divide by the coverage on the tin. A typical bedroom of 3.5 × 4 m with 2.5 m walls needs about 7–8 litres for two coats.
Two coats is the norm for an even finish. One coat can be enough when repainting the same colour; three may be needed when covering a much darker colour or fresh plaster.
Most wall paints cover 8–12 m² per litre per coat (about 350–400 ft² per gallon). Rough, porous or unpainted surfaces absorb more, so use the lower figure.
This calculator covers walls only. For a ceiling, run it again with the room length as the 'wall length' and the room width as the 'height', set doors and windows to 0, and use ceiling-paint coverage.
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