Buying the right amount of paint saves money and time. Here is the formula the professionals use.
Step 1: Measure the walls
Multiply each wall’s width by its height (in metres) and add them together. A room 4 m × 5 m with 2.7 m ceilings has 2 × (4 + 5) × 2.7 = 48.6 m² of wall.
Step 2: Subtract doors and windows
Allow about 1.9 m² per door and 1.5 m² per window.
Step 3: Multiply by coats
Two coats are standard for good colour and durability.
Step 4: Divide by coverage
Most emulsions cover around 10–12 m² per litre per coat on smooth surfaces. Rough blockwork and fresh plaster absorb more — add 15–25%.
Example: 45 m² × 2 coats ÷ 11 m²/L ≈ 8.2 L → one 20 L bucket covers this room with plenty left for touch-ups.
Use our calculator
Skip the maths with the free IBC paint calculator, which also suggests the most economical bucket sizes and adds them straight to your quote.
Ready to start your project? Browse our products, explore colours, or request a free quote — we’ll email you pricing within one business day.
