Paint Calculator
Estimate how much paint a room needs, allowing for coats, doors and windows.
Processing: This tool runs entirely in your browser. Your input and any file you open stay on your device — nothing is uploaded to a server.
How to use the paint calculator
- Fill in the fields — they start with a worked example.
- Read the answer, and the arithmetic shown beneath it.
- Copy the results, or adjust the inputs to compare scenarios.
About this tool
Wall area is the perimeter times the height, less the doors and windows. Multiply by the number of coats and divide by the coverage on the tin — usually 10 to 12 square metres per litre for emulsion, less on bare or porous surfaces.
A standard door is about 1.8 m² and a window about 1.5 m², which is what the deductions use. Bare plaster, strong colour changes and textured surfaces all drink more paint than the tin claims, so the estimate includes a small allowance and it is still worth buying slightly over rather than matching a batch later.
Common uses
- Buying the right amount of paint for a room.
- Estimating cost before starting a decorating job.
- Checking a decorator's quantity.
Frequently asked questions
- How many coats do I need?
- Two on previously painted walls in a similar colour; three when covering a dark colour with a light one, or painting bare plaster.
- Does this include the ceiling?
- No — this is wall area only. Ceilings are usually calculated separately as length × width.
Related tools
Area Converter
Convert between square metres, square feet, acres, hectares and square miles.
Tile Calculator
Work out how many tiles a floor or wall needs, including a wastage allowance.
Length Converter
Convert between millimetres, centimetres, metres, kilometres, inches, feet, yards and miles.
Percentage Calculator
Work out a percentage of a number, what percentage one number is of another, and percentage change.