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 (water-based): 14 m²/L — modern acrylic eggshell for woodwork and walls
• Eggshell (solvent/oil): 10 m²/L — traditional oil eggshell, which covers noticeably less
• Gloss: 14 m²/L — high-sheen finish typically used on wood and metalwork

These are conservative real-world working rates, derated from manufacturers' published “up to” maxima (for example Dulux Trade Vinyl Matt up to 17 m²/L, Dulux Diamond Eggshell up to 16, and Dulux Quick Dry Gloss up to 16) so you don't under-order. Traditional solvent-based eggshell is the exception — its manufacturer figure is only 8-10 m²/L, so pick the right eggshell type. Actual coverage varies with 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.