The coverage figure on a paint tin is measured under close-to-ideal conditions: smooth, primed, similar base colour. Real walls rarely match all three, which is why the litres you actually use often exceed the litres the tin's maths predicted.
| Factor | Effect on coverage |
|---|---|
| Textured or porous surface | Up to 30% more paint needed |
| Bare, unprimed plaster | Extra mist coat required |
| Major colour change (e.g. dark → light) | Often needs a 3rd coat |
| Premium vs standard emulsion | ~12 m²/L vs ~14 m²/L |
A 4m × 3.5m room with 2.4m walls, one door and two windows needs 31.6 m² of paintable area. At two coats and 13 m²/litre, that's 4.86 litres — two 2.5L tins. On a textured wall or a big colour change, the real usage can climb 20-30% past that baseline, occasionally tipping into a third tin.
Rounding up to the next full tin, rather than buying the bare litre estimate, isn't just a safety margin — paint batches can vary slightly in colour between production runs, so having enough from one batch to finish the whole room in one pass avoids a visible seam where an older and newer batch meet.
Room dimensions and door/window count in — exact litres and the best tin combination out.
Use the Paint Calculator →