Paint calculator
How much paint a room needs, allowing for doors, windows and the number of coats.
How it works
Enter the room dimensions and this works out the wall area, subtracts doors and windows, and converts to litres or gallons at a realistic spread rate.
The spread rate is where estimates go wrong. Tin labels quote a best case on a smooth, sealed, similarly coloured surface \u2014 typically 12 to 14 m² per litre. Real walls take more. Bare plaster drinks the first coat, textured or previously unpainted surfaces need noticeably more, and a strong colour change often needs three coats rather than two. The default here is deliberately more pessimistic than the tin.
Two coats is the working assumption for a repaint in a similar colour. Going from dark to light, or covering bare plaster, plan for a primer or mist coat plus two topcoats.
Buying slightly over is the cheaper mistake. A part-used tin seals and keeps for touch-ups; running out mid-wall leaves a visible join, and a later batch may not match exactly.
This tool runs entirely in your browser. Nothing you enter is sent to a server, logged or stored, and the page keeps working with the network disconnected.
Common questions
- How much paint do I need for a room?
- Roughly the wall area divided by 11 m² per litre, then multiplied by the number of coats. A typical 4 × 3 m room with 2.4 m ceilings needs about 6 litres for two coats.
- How many coats of paint do I need?
- Two over an existing similar colour. Three, or a primer plus two, when covering bare plaster or making a large colour change.
- Why does the tin say it covers more than this calculator assumes?
- Tin figures are a best case on smooth, sealed, similarly coloured surfaces. Porous, textured or bare surfaces absorb considerably more.
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Sources
- Typical range compiled from manufacturer specifications — At One Place