How the paint calculator works
It adds the four walls — 2 × (length + width) × wall height — and optionally the ceiling. Standard door and window areas are deducted, then the result is multiplied by the number of coats and divided by the paint coverage.
Coverage is the area one litre or gallon covers. It is printed on the can and depends on the paint, surface and colour; smooth primed walls need less paint than porous or textured walls.
Before you buy
- Round up to whole cans. Leftover paint is useful for touch-ups.
- Check the coverage on the can, not a generic average.
- Primer is not included. Bare or dark walls may need a primer coat first.
Assumptions
Standard door 1.8 m², standard window 1.5 m². The ceiling is included only when checked. Primer, trim and labour are not included.
Last reviewed October 27, 2026
Frequently asked questions
How much paint do I need for a 4 × 5 m room?
With 2.5 m walls, one door, one window and two coats at 10 m²/L, about 12.3 L. Buy 4 × 3.78 L cans.
Should I subtract doors and windows?
Yes. This calculator deducts 1.8 m² per door and 1.5 m² per window for a more realistic estimate.
How many coats should I use?
Two coats are typical for a colour change. One may be enough for a similar colour; strong colours often need three.
How much extra paint should I buy?
Round up to whole cans. A little leftover paint is useful for touch-ups and future repairs.