I am writing a PhD thesis in literature. I have covered all areas in about 120 pages. Does the length of a PhD thesis matter even if it has covered all the areas mentioned in the synopsis?
The advice you have so far is pretty US specific - in a system without a committee system, where you will be judged by your examiners in a one off thing, you may want to be more careful.
Of course, the person who should really know the answer to this is your supervisor/advisor, but should also be able to look up what the criteria are for your university. I would generally ask around your field. In my field in my country, a thesis is expected to contain at least three more or less complete "stories" that add up to a advance in the field. In biomolecular sciences, 120 pages would be very much on the short side for that, but not completely out of the question - a 40 page literature review and 20 pages of Methods, 5 pages of general discussion/conclusion would leave you with only 55 pages of results - doable if you are terse and everything worked first time.
But these expectations are going to differ from system to system and subject to subject. Speak to people in the know.
I did one in the low hundred plus. As long as it passes your committee that is all that matters. But a brave face on, submit it and see the reaction.
Don't even ask if it is suitable. Just submit it to your advisor as your intended work product. After all your independent view is that it is good enough. Let him volunteer a criticism if he chooses. But don't suggest it.
If it satisfies your advisor and the committee it is fine. A 1 page dissertation in poetry is within the realm of possibility, however unlikely.
It is a mistake to pad things, I think.
Some places (and some advisors) might have minimal length requirements, though I would question them. But if that is the issue here you need to think a bit more about the overall structure, not just the page count.