What "paint coverage" actually means
Why the same litre of paint never covers quite the same area from one job to the next.
A reference value, not a guarantee
A paint's coverage rate, given in m²/L (or sq ft/gal), tells you the surface a litre theoretically covers in a single coat. It's a manufacturer or category reference figure, established under standardised conditions — a flat surface, average absorption. On a real job, the coverage you actually get almost always differs a little from that reference.
What makes real-world coverage vary
- Surface porosity. A new render or bare plaster absorbs more than an old, sound coat of paint: the first coat simply doesn't spread as far.
- Application technique. Roller, brush, or sprayer don't lay down the same film thickness; a well-set-up sprayer gets closer to the reference figure, while a brush tends to lay it on thicker.
- Dilution. Thinned paint spreads further but covers less well — that's not a real gain, just a trade against the number of coats you'll need.
- Colour contrast. A big shift in shade (especially dark to light) often needs an extra coat, which affects total consumption even though the per-coat rate doesn't change.
How the calculator uses it
You never enter the coverage rate yourself: it's worked out automatically from the paint you pick, using our validated technical database. Consumption per coat follows directly (1 ÷ coverage), then gets multiplied by the actual surface and the number of coats to give the quantity before margin.
Take the category average used for acrylic paint: 10 m²/L, which means 0.1 L/m² per coat.
Limits
Our reference value remains a category average, not a specific commercial product's data sheet. If you've already picked a particular brand's product, its own data sheet stays the most reliable source for that exact item.