"Summing up years of work in one sentence." That's the tagline for Lol My Thesis, where PhD candidates (Edit: and undergrads) make fun of their own theses by reducing them to just a sentence or two.
Though page number is obviously far less important than the content and quality of one's work, it is nevertheless very common for PhD candidates to obsess over the length of their theses. How many pages should it be? How long are other people's theses? Short answer: it varies. And by more than you may realize.