How Much Paint Do I Need?

Start with wall area, not floor area

Paint covers walls, so the number that matters is the perimeter of the room multiplied by the ceiling height. For a 4 × 3.5 m room with 2.7 m ceilings that is 2 × (4 + 3.5) × 2.7 = 40.5 m².

Only subtract openings bigger than about 1 m². A standard door is roughly 1.9 m² and an average window 1.5 m².

Coverage is per litre, per coat

Most interior emulsions state 10–12 m² per litre on smooth, sealed surfaces. Bare plaster, new drywall and textured walls can drop that to 7–9 m².

Multiply the paintable area by the number of coats before dividing by coverage. Two coats is the normal answer.

Then convert to cans

You cannot buy 8.6 litres. Cans come in 1 L, 4 L, 5 L and 10 L. Two 4 L cans plus one 1 L can gets you 9 L with 0.4 L spare — worth keeping for touch-ups.