Frequently asked questions
How the calculator works, what it does automatically, and what it will never do (like inventing a technical value).
How does the calculator work out coverage and number of coats?
The reference coverage rate (in m²/L or ft²/gal) is the one for the paint you select, read from the calculator's technical database. Coats follow a general rule: two finish coats, whatever the surface. For a one-coat paint, the single-coat quantity is given as well. These are outputs of the calculation, never values you type in.
Why can't I enter the coverage rate or number of coats myself?
Because they're technical values tied to the paint you chose, not personal estimates. Making them editable would risk results that no longer match the selected product; if your paint's data sheet gives a different coverage rate, the data sheet is what counts.
The result says "technical data pending validation" — what does that mean?
It means the database doesn't yet hold a verified value for the wall and paint combination you chose. Rather than show an approximate figure, the calculator says so plainly. The database is filled in as values are checked.
How are doors and windows deducted from the surface?
You enter the gross wall surface, then add each opening by its width and height. The calculator adds up their areas and subtracts them to get the surface you actually paint; if the openings exceed the surface entered, it says so instead of calculating.
Do I have to specify the wall type?
Yes. You choose the wall type before the paint: it narrows the list to paints that suit that surface. If yours isn't listed, choose "Other": every interior paint stays available, with a note that the estimate may be less precise.
My wall isn't in the list — what should I do?
Choose "Other" and describe it in a sentence. The engine never invents a compatibility for a surface it doesn't recognise — it applies general rules and flags this clearly.
Does switching units (metric, US imperial, UK imperial) change the result?
No. The engine always calculates in fixed internal units and only converts what's displayed. Switching between systems never changes the underlying maths.
What's the safety margin for?
It's added after the technical calculation (coverage, coats, surface) to cover normal application losses. It never changes the coverage rate or the number of coats — only the final recommended quantity.
Is what I enter saved anywhere?
The calculator runs entirely in your browser: nothing you type is sent to a server. See our privacy policy for details.
Is the site available in other languages?
Yes — the calculator, guides and FAQ are available in 6 languages: French, English, Spanish, Portuguese, Italian and German. Use the language switcher to change.