Paint calculator

How the amount of paint is calculated

litres = area × coats ÷ coverage · with reserve = litres × (1 + reserve ÷ 100) · cans = rounded up (litres ÷ can size)

Paint is not measured per room but per surface you actually roll over. First you get the net wall area (plus the ceiling if you are painting it), then multiply it by the number of coats and divide by the coverage in square meters per litre.

If you do not know the area yet, work it out in the area calculator — its Walls mode gives the net area with doors and windows already deducted.

Finally a reserve is added for touch-ups and the amount is divided by the can size. The number of cans is always rounded up, because you cannot buy half a can.

What coverage (m²/L) means and how many coats to use

Coverage says how many square meters one litre covers in a single coat. The figure is printed on the tin and differs from paint to paint, so copy it from your own label — the value offered in the calculator is only an example meant to be replaced.

The number of coats depends on the substrate and on how well the paint covers. Refreshing the same shade often works in one coat, while a new shade or painting over a darker colour usually takes two. The calculator multiplies the area by the coats, so two coats mean twice the paint.

Worked example: a 4 × 3 m room

A 4 × 3 m room 2.6 m high has a 14 m perimeter and 36.4 m² of gross wall. A 0.9 × 2.05 m door and a 1.4 × 1.2 m window make 3.525 m² of openings, leaving 32.875 m² of net wall.

With two coats you cover 32.875 × 2 = 65.75 m². At a coverage of 10 m²/L that is 6.58 L, and with a 10% reserve about 7.23 L. You buy 3 cans of 2.5 L, so 7.5 L, with roughly 0.27 L left over.

If a 2.5 L can costs 25 KM, the paint for this room costs 75 KM. Prices differ by brand and by shop, so enter your own price to get a real figure.

Why rough and absorbent walls drink more paint

A rough, porous or never-painted surface absorbs more paint than a smooth, already-painted wall, so the same can covers fewer square meters than the label suggests. The same goes for fresh plaster and plasterboard, where a primer cuts the absorption and the amount of topcoat needed.

That is why the result is a planning estimate rather than a guarantee. The calculator uses the coverage you entered, rounds cans up, shows quantities to two decimals, deducts openings at their full area and charges labour per m² of surface — not per coat.