Take a look at the following captions and see if you notice anything unusual:
Et si vous regardez bien au deuxième étage,
And if you look closely at the second ["third" in the US] floor,
il y a une magnifique frise.
there is a splendid frieze.
Caption 14, Voyage dans Paris - Butte Montmartre
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Donc vous voyez la petite lumière rouge en...
So do you see the little red light in...
au premier étage?
on the first ["second" in the US] floor?
Caption 32, Mon Lieu Préféré - Rue des Rosiers
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Although it might seem like we’ve made some errors in our translations, the number discrepancy you see is actually completely accurate. This is because the floors of French buildings are not numbered in the same way that American floors are.
As you can see, a given French floor is always one number lower than a given American floor: le deuxième étage corresponds to the third floor, not the second, and le dix-huitième étage corresponds to the nineteenth floor, not the eighteenth.
The explanation for this is simple: the French (and most other Europeans) don’t count the ground floor of a building when numbering its stories, whereas Americans do. The French word for "ground floor" is rez-de-chaussée, and the floor above le rez-de-chaussée is le premier étage (the second floor). In American English, "ground floor" and "first floor" are generally synonymous and thus can both be used for rez-de-chaussée. So when you’re in a French elevator, instead of seeing a button marked "G" for "ground floor," you’ll see one marked "RC" for rez-de-chaussée.
Note, however, that French-Canadian speakers have adopted the US system, so you won't have to worry about subtracting floor numbers when you're in Quebec (you can learn some more about Canadian French in this lesson). You'll notice this when listening to Annie Chartrand, a French-Canadian musician, describe her childhood home:
J'habitais au deuxième étage avec mes parents
I lived on the second floor with my parents
et au premier étage, c'était un bar taverne...
and on the first floor, there was a bar-tavern with...
Captions 24-25, Annie Chartrand - Sa musique
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Here is a little table to review:
In France | In the U.S. | In Quebec |
le rez-de-chaussée | first floor | le rez-de-chaussée/le premier étage |
le premier étage | second floor | le deuxième étage |
le deuxième étage | third floor | le troisième étage |
Therefore, a three-story house in the US (first floor + second floor + third floor) is the same as une maison à deux étages in France (rez-de-chaussée + premier étage + deuxième étage) and une maison à trois étages in Quebec (rez-de-chaussée/premier étage + deuxième étage + troisième étage).
To make this a bit easier, you could take the word étage to mean specifically an upstairs floor in France. Indeed, one way of saying "upstairs" in French is à l’étage (the other way is en haut, while "downstairs" is en bas). In that case, le premier étage could be translated more precisely as "the first upstairs floor," i.e., the second floor.
A side note: To remember the word rez-de-chaussée, a bit of etymology might be useful. Une chaussée is another word for "road," and rez is Old French for ras, meaning "flat" or "level" (think of the word "razor"). The ground floor is called le rez-de-chaussée in French because it is level with the road.
And for an in-depth discussion of floor numbering around the world, see this Wikipedia entry: https://en.wikipedia.org/wiki/Storey#Numbering