What is the Paint Calculator?
The paint calculator estimates the litres of paint needed to cover the walls of a room, allowing for doors, windows and the number of coats.
How to use the Paint tool
- Enter Total wall length (perimeter), Wall height, Coats and Coverage.
- The result updates instantly as you type, or press Calculate.
- Use Try an example to see how it works, and Reset to start again.
Formula
Area = perimeter × height − openings. Paint = area × coats ÷ coverage per litre.
Worked example
With total wall length (perimeter) 14 m, wall height 2.5 m, doors and windows area 4 m², coats 2, coverage 10 m² per litre, the paint needed comes to 6.2 litres. Paintable area: 31 m²; With 10% extra: 6.8 litres.
Frequently asked questions
How much does a litre of paint cover?
Most wall paints cover 8 to 12 m² per litre per coat. Check the tin.
Should I buy extra?
Yes. About 10% extra covers touch-ups and uneven surfaces.
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Checked by Calcovate · Formula tested against worked examples · Updated 7 Nov 2026 · How we check our calculators.