How is the quantity calculated exactly?
Net area (length × width minus doors and windows) × number of coats ÷ coverage rate (m² per liter). The default rate of 10m²/liter per coat is a common average for most approved water-based paints, but you can adjust it to match the actual can you'll buy (usually stated on the back of the can).
Why is two coats the most common?
The first coat rarely covers the old base color completely and evenly, especially when changing a dark color to a light one or vice versa. The second coat ensures even coverage and better color durability over the long term.
Does the calculation include a primer coat?
No, the calculator only calculates the final (color) paint coats. If the surface is new (unpainted block or plaster), you'll typically also need a separate primer quantity at a roughly similar coverage rate — add it as an extra coat if you need a rough estimate for it.
Why does the calculator suggest cans of different sizes instead of a single liter number?
Because paint is practically sold in standard cans (18-liter gallon, 4-liter quarter-gallon, 1 liter), so buying the fewest possible cans that cover your actual need is cheaper than buying several scattered small cans.
What if I have more than one wall or room?
Calculate each surface separately if their dimensions differ, or manually sum all the lengths and areas before entering if the surfaces are similar (like the same height for several walls), and enter the total as a single "length × width" representing the total area.
