I know how many people were at Hogwarts, but I don't know how many rooms are there totally.
An indeterminate number
Hogwarts is a magical castle with stairs and hallways that rearrange themselves and at least one room that is documented to vanish when not needed (the Room of Requirement), and quite possibly more.
Also, Rowling is notoriously terrible with math (especially population math) and has said that she deliberately instituted the fluid architecture so that she didn't have to worry about where things were. In other words, she specifically designed Hogwarts to avoid having to answer this question (among others).