Paint Calculator
Work out how much paint you need for a room’s walls and ceiling – in litres and tins.
Result
Enter the room size.
How it works
Wall area
2 × (length + width) × height
Minus any doors and windows you enter.
Paint needed
area × coats ÷ coverage
A 4 × 3.5 m room with 2.4 m walls, less 3.5 m² of openings, needs 32.5 × 2 ÷ 12 = 5.4 litres.
The default of 12 m² per litre is deliberately a little below what makers quote for standard matt emulsion (Dulux retail matt says “up to” 13–14 m² per litre; trade paints up to 16–17), because those figures assume smooth, sealed walls. Always check the tin and use its figure. Woodwork paints such as gloss and eggshell cover a different area and are worked out separately.
Frequently asked questions
How much does a litre of paint cover?
Most interior emulsions cover about 10–14 m² per litre per coat on smooth, sealed walls. It’s printed on the tin – use that figure. Textured or porous surfaces take more.
How many coats do I need?
Two coats is usual for an even finish. Bare plaster needs a mist coat first, and a big colour change (especially light over dark) may need three.
Do I need to subtract doors and windows?
It’s optional. Leaving them in gives you a little spare paint for touch-ups, which is often useful.
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