Paint Coverage Calculator

Work out how many litres of paint you need for a room, and how many tins to buy, based on the wall area, number of coats and the paint's own coverage rate.

Default coverage of 15m² per litre is a typical figure for trade matt emulsion on a smooth wall — check your chosen paint's own tin or datasheet for its exact figure and use that instead if you have it.

Area to paint 0.0 m²
Paint needed 0.0 L
5L tins 0
2.5L tins 0

How This Is Calculated

The calculator starts with the wall area: two widths plus two lengths, multiplied by the wall height, with the ceiling area added on top if you choose to include it. It then deducts an average area for each door (1.5m²) and window (1.2m²) you enter, since these obviously don't need painting.

That net area is multiplied by the number of coats, then divided by the coverage rate to get the total litres of paint needed. Selecting "new plaster or bare surface" sets the default number of coats to 3 rather than 2, reflecting the standard practice of a diluted mist coat followed by two full coats on porous, unpainted surfaces — you can still adjust the coat count manually if your situation is different.

The litre figure is then rounded up to whole 5L and 2.5L tins, since it's always better to have a little paint left over from the same batch for touch-ups than to run out mid-wall.

Common Questions

Why does the calculator ask for a coverage rate instead of just giving one figure?

Coverage varies by paint, typically 14-17m² per litre per coat for a standard trade matt emulsion on a smooth, previously painted wall. Every tin states its own coverage on the label or datasheet, so that figure will always be more accurate than a generic average - use it if you have it.

How many coats do I need on new plaster?

New or bare plaster is porous and soaks up far more paint than a previously painted wall, so the usual approach is a diluted mist coat first (roughly 10% water added, applied thinly) followed by two full coats - three coats in total rather than the usual two. That's why this calculator defaults to 3 coats when you select new plaster.

Should I deduct doors and windows from the area?

Yes, for an accurate figure. This calculator uses an average deduction of 1.5m² per door and 1.2m² per window, which is close enough for most standard rooms. For an unusually large window or a floor-to-ceiling glazed door, adjust the room area directly instead.

Is it worth buying an extra litre over the exact calculated amount?

Yes. Paint batches can vary slightly between tins, and having a little extra means touch-ups later use paint from the same batch rather than a different one that may not match exactly. Round up to the next full tin size rather than trying to buy the exact litre count.

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