Calculate how much paint you need for walls, ceilings and trim based on room dimensions.
This paint calculator works out how much paint you need for a room or wall, deducting doors and windows and allowing for multiple coats. It reports litres and US gallons so you can buy the right amount wherever you are.
| Paint | Coverage per litre |
|---|---|
| Emulsion / latex (walls) | ~10–12 m² |
| Primer / undercoat | ~10 m² |
| Gloss / trim | ~12–15 m² |
A 4 m × 3 m room with 2.4 m walls has a perimeter of 14 m × 2.4 = 33.6 m². Two coats = 67.2 m²; at 11 m² per litre that's about 6 litres (roughly 1.5 US gallons).
A 12×12 ft room with 8 ft ceilings has about 384 sq ft of wall area. After deducting doors/windows, you'll need roughly 2 gallons for 2 coats.
Most projects need 2 coats for even coverage. Going from a dark to light colour may require 3 coats or a tinted primer first.
No – this calculates wall paint only. For ceilings, multiply length × width and divide by the coverage rate.
Use primer on bare plaster, new wood or metal, or when making a big colour change. On fresh plaster, a watered-down mist coat seals the surface before your top coats go on.
Around 10–12 m² per litre per coat on smooth walls; rough or absorbent surfaces cover less. The calculator uses a realistic spread rate.
