Work out how many litres you'll need — wall area and coats in, litres out, with deductions for doors and windows.
How this works
Paint coverage is given as m² per litre on the tin. This works out your paintable wall area (minus doors and windows), multiplies it by how many coats you're doing, and divides by that coverage rate to land on the litres you'll need.
What are you painting?
A whole room, or just one wall?
Grab a tape measure — roughly is fine.
All 4 walls: 36.0 m²
Doors & windows
These don't get painted, so they come off the total. Leave at 0 if none.
A standard interior door is roughly 1.6m², an average window around 1.5m² — adjust if yours are bigger or smaller.
Coats
Two coats is standard for most jobs — dark or bright colours often need a third.
Paint & coverage rate
Pick your brand, or enter a custom spread rate from the tin.
Readout
32.9m² net area · 2 coats
4.5 L
estimated paint needed
Using 16.0 m²/L coverage
Gross wall area36.0m²
Door/window deductions3.1m²
Net paintable area32.9m²
Total area (× 2 coats)65.8m²
Gross vs net area: gross is the full wall area if it were a blank canvas; net subtracts doors and windows, since paint doesn't go on glass or timber. The litres figure is based on net area × your number of coats.
Coverage rates vary: the figures here are the brand's own published spread rates for a typical low-sheen interior product — real coverage depends on the surface (bare plasterboard soaks up far more than a previously painted wall), the colour (deep reds and yellows often need an extra coat regardless of brand), and application method. The number on your actual tin is the one that matters — treat this as a shopping guide, not a guarantee.
Priming bare surfaces: if you're painting bare plasterboard, new render, or a big colour change, factor in a sealer/undercoat coat separately — primers typically cover less per litre (around 10–12 m²/L) than topcoats.