Yes, both are correct and can be used. When you have a choice of numbers you can either say 'what' or 'which.' One is not better than the other.
That's exactly what I'm up to! There was no statement about the house so I took "what" and not "which".I know your building has more than one floor. Which floor do you live on?
I don't know anything about the building. What floor do you live on?
But you'd only say that if you know the number of floors the house has (as you wrote), wouldn't you?So, for this specific example I'd say:
"Which floor do you live on?" (as in which one? which? You wouldn't ask what one?)
"I live on the second floor."
Is it of importance? I knew that the answer is "on the second floor".But are you saying you only found out about the second floor after you had the opportunity to fill in the blank?
Hmm, that stands in contrast with what Siberia said. Is it a BE/AE thing?
But "what" doesn't sound weird enough to be looked at oddly, does it?But the which version seems most natural.
Your perspective may be due to the fact that the questioner is unconciously picturing a typical office building while asking. Search me!I wonder why?
Very perceptiveOld, but interesting discussion.
When I'm in the same elevator or buidling, I would naturally say: "Which floor do you live on?" as the number of floors are limited.
However the number of floors are never mentioned during the conversation. The question also doesn't specify the building itself, and I'm myself not aware of how many floors that apartment block actually has. Therefor: "What floor do you live on?" works perfectly fine for me as well.
If I meet somebody on the street and he/she tells me that he/she lives somewhere in Manhattan, I would probably ask "What floor do you live on?". Simply because I don't know how many floors the apartment has. In this situation "Which floor do you live on?" sounds a bit awkward, because I don't even know the building (Just imagine the answer would be "floor 3.5").