Paint Calculator — How Much Paint Do You Need?
Getting the right amount of paint before you start saves you a second trip to the hardware store — and avoids running out mid-coat. This calculator works out the paintable wall area, applies your chosen waste allowance, and tells you how many cans to buy.
How we calculate
Wall area = 2 × (length + width) × height. Doors (~1.9 m²) and windows (~1.2 m²) are subtracted. Paint = (paintable area ÷ coverage per litre) × coats × (1 + waste %). Cans = ⌈paint litres ÷ can size⌉.
Worked example
A 4 m × 3 m room with 2.4 m ceilings, one door, one window, two coats at 12 m²/L with 10% waste: wall area ≈ 33.6 m², paintable area ≈ 30.5 m², paint needed ≈ 5.6 L, so 3 × 2.5 L cans.
Common mistakes
- •Not accounting for doors and windows — this typically overstates paint needed by 10–15%.
- •Using only one coat for a colour change over a very different base colour.
- •Forgetting primer when painting over bare plaster or a dark colour.
- •Buying single large cans when the remainder cannot be resealed easily.