How much paint do I need?

The formula is simple: area × coats ÷ coverage. What matters is the coverage printed on the tin and the surface you paint.

1. Measure the area

Wall area = room perimeter × room height. Subtract doors and windows; leave small openings under about half a square metre in – they make up for the extra paint used on edges.

2. Read the coverage on the tin

Coverage tells you how many square metres one litre covers per coat – for interior emulsion usually around 6 to 8 m²/l. In the EU it is linked to the hiding power classes of EN 13300: the manufacturer states the coverage at which the paint reaches a given class (class 1 hides best, class 4 least). Use the coverage stated on your tin.

3. Surface and coats

Smooth, already painted walls absorb little. Woodchip and plaster need more, rough or new plaster and fresh plasterboard considerably more – the calculator uses factors of 1.0 / 1.15 / 1.3. A colour change, strong shades or patchy walls need two, sometimes three coats; absorbent surfaces often need a primer first.

Worked example

Living room 5 × 4 m, height 2.5 m, one door, two windows, woodchip, two coats, coverage 7 m²/l, 10 % extra:

• Gross wall area: 18 m × 2.5 m = 45 m²
• minus door and windows: 5.02 m² → 39.98 m²
• Paint: 39.98 × 2 × 1.15 ÷ 7 × 1.1 = 14.45 l → 1 × 10 l + 1 × 5 l
• Ceiling (20 m²): 7.23 l → 1 × 5 l + 1 × 2.5 l

Calculate with your own measurements

Choosing tin sizes

A large tin usually costs less per litre than several small ones. That is why the calculator does not simply look for the smallest quantity, but for a combination with little left over and few tins. Opened paint keeps well if sealed and stored frost-free – handy for touch-ups later.