Paint coverage rates
What a litre of paint actually covers on each kind of surface, why the first coat is different from the rest, and how to read the number printed on the tin.
The table
| Surface | m² per L | ft² per US gal | First coat | Primer needed |
|---|---|---|---|---|
| Previously painted, smooth and sound | 12.0 | 489 | full | No |
| New plaster or skim, sealed | 10.0 | 407 | ×0.75 | Mist coat |
| New plasterboard / drywall | 10.0 | 407 | ×0.75 | Yes |
| Textured, artex, heavy roll finish | 8.0 | 326 | ×0.85 | No |
| Render, brick, rough masonry | 6.0 | 244 | ×0.70 | Yes |
| Wood trim, doors, joinery | 14.0 | 570 | ×0.85 | Yes on bare wood |
| Metal, radiators, railings | 14.0 | 570 | full | Yes, correct type |
Imperial figures are US gallons. A UK imperial gallon is about 20% larger, so a British tin quoting "square metres per litre" is the number to use, not the US gallon column.
Why the first coat is a separate calculation
A porous surface absorbs paint. Bare plaster, new plasterboard, sanded filler and bare wood all pull the liquid out of the first coat, leaving less on the surface as film. The paint has not disappeared — it is inside the wall, doing nothing useful for the finish. On new plaster the first coat covers roughly three-quarters of what the same paint covers on a wall that has been painted before.
Two coats on new plaster therefore does not cost you 2 × area ÷ coverage. It costs you:
litres = area / (coverage × 0.75) + area / coverage
On a 60 m² room at 10 m²/L that is 8.0 + 6.0 = 14.0 litres, where the naive calculation says 12.0. Two litres is most of a tin, and it is exactly the amount people find themselves short of on a Sunday afternoon.
This is also what primer is for. Primer is formulated to seal the surface cheaply, so the expensive finish coat is not absorbed. If you prime, the first-coat penalty disappears and the finish paint behaves as it would on a previously painted wall.
Reading the tin
Manufacturers publish coverage measured under controlled conditions: a smooth, sealed, primed test panel, a specified wet film thickness, a laboratory temperature. It is a real number and it is not dishonest — it is simply the best case, and it is not what a roller on a bedroom wall achieves.
The gap comes from four places:
- Film thickness. A roller lays down a thicker and less even film than a lab applicator. Thicker film, less area per litre.
- Surface texture. The real surface area of a textured wall is larger than its measured area. Artex or a heavy roll finish can add 20% to the true area without changing the tape measure at all.
- Absorption. Covered above.
- What never reaches the wall. Paint left in the tray, in the roller sleeve and on the brush. On a small job this is a surprisingly large percentage.
Treat the tin figure as a ceiling. If you want to plan against it anyway, use it for coat two and onwards and keep the absorption factor for coat one.
How many coats
| Situation | Coats | Notes |
|---|---|---|
| Refreshing the same colour | 1 | Only if the existing surface is sound and clean. Any patching needs spot-priming first or it will flash. |
| Light colour over light colour | 2 | The normal case. |
| New plaster or board | 2 + mist | Mist coat, then two full coats. |
| Dark over light | 3 | Or two over a grey-tinted primer, which is usually cheaper and more reliable. |
| Light over dark | 3–4 | Use a white or light grey primer first. Emulsion alone can take four coats to bury a strong colour. |
| Strong red, orange or yellow | 3–4 | These pigments have genuinely poor opacity. Tinted undercoat is not optional here; without it four coats is common. |
Deducting openings — the decorator's rule
Trade estimators do not deduct openings under about one square metre, and it is not carelessness. Cutting in around a frame with a brush uses more paint per square metre than rolling open wall, and it takes far longer. The paint you save by not covering the glass is roughly the paint you spend cutting in around it, so the two cancel.
Deduct full-height glazing, patio doors, a large picture window, an open archway. Do not deduct a normal window, an internal door, or a serving hatch. Systematically deducting every small opening is a reliable way to end up a litre short.
Box your tins. If a room needs more than one tin of the same colour, decant them all into one larger bucket and stir before you start. Factory batches of the same colour code vary slightly. Starting a new tin halfway up a wall puts that variation in a vertical line down the middle of the room, and you will see it every time the light changes.
Common mistakes this table is designed to catch
- Using the tin figure for a first coat on new plaster. The single most common shortfall, and worth about 20% of the total.
- Forgetting the ceiling is a different product. Ceiling paint is a flat matt; wall paint is usually a different sheen and sometimes a scrubbable grade. Price them separately.
- Buying trim paint by the same logic as wall paint. Joinery covers at 14 m²/L and a room's worth of trim is only a few square metres. One litre goes a very long way; the usual error is buying 2.5 litres and throwing most of it away.
- Ignoring the sheen change. The same colour in matt and in eggshell reads as two different colours. Do not use up leftover matt as a "first coat" under eggshell and expect an even finish.
Use it
The paint calculator applies every figure on this page, works out the best combination of tin sizes to buy, and separates the first coat from the rest automatically.
Last reviewed 2026-09-18. Coverage figures are practical working rates for planning. Your paint's technical data sheet is the authority for that product.