Paint Coverage Calculator — How Much Paint Do I Need?

Our paint coverage calculator works by first calculating the total wall area of your room from its dimensions, then subtracting openings (doors and windows) to get the net paintable area. This is then multiplied by the number of coats and divided by the coverage rate for your chosen paint type.

The formula

Litres needed = (Net wall area × Number of coats) ÷ Coverage rate per litre × Wastage factor

Net wall area = (2 × (Length + Width) × Height) − (Doors × 1.8 m²) − (Windows × 1.2 m²)

For example, a room 4m × 3.5m with 2.4m ceilings, one door and two windows: Wall area = 2 × (4 + 3.5) × 2.4 = 36 m². Minus 1 door (1.8 m²) and 2 windows (2.4 m²) = 31.8 m². For 2 coats of matt emulsion at 12 m²/L: 31.8 × 2 ÷ 12 = 5.3 litres, plus 10% wastage = 5.8 litres.

Coverage rates we use

• Matt Emulsion: 12 m²/L — the most popular finish for walls and ceilings
• Silk Emulsion: 14 m²/L — wipeable finish, popular for kitchens and hallways
• Eggshell: 16 m²/L — durable mid-sheen finish for woodwork and walls
• Gloss: 17 m²/L — high-sheen finish typically used on wood and metalwork

These rates are based on manufacturer guidelines from Dulux and Crown for smooth, sealed surfaces. Actual coverage will vary depending on surface porosity, texture and application method (brush, roller or spray). We recommend adding 10% for wastage to account for loading rollers, cutting in and general spillage.