Plural or singular? After the word "any"

Question

I often get confused which one to use after any. Or are both correct?

Do you have any room available on March 22nd?

Do you have any rooms available on March 22nd?

Answer 1

In this use of "any", in a question, the plurality distinguishes between mass and count nouns.

Hence, "any room" means "any space". You could ask:

Is there any room for my backpack? I want to set it down.

Whereas "any rooms" is the count noun you want to use:

Are there any rooms available? I want to book one for this weekend.

That said, the singular would be understandable with enough context. It would just be less likely given that the plural is unambiguous.

Do you have any room that sleeps six people? *(I am forced to reinterpret "room" when I hear "sleeps".)

Note that this is not true of "any" in a declarative sentence. These sentences both refer to the count noun "hotel room" despite being in the singular:

Any room will do, as long as it has a bed!

I don't know of any room that includes a hot tub.