IITs collectively have only 33k undergrads, according to wikipedia:
https://en.wikipedia.org/wiki/Indian_Institutes_of_Technolog...
That would make the entire system comparable to a large state school in the US. They do have proportionally more grad students, so total student body is right around the biggest state schools - Florida, Texas, Ohio, etc.
Definitely not on the same level as Stanford or Harvard, but still very impressive.