It’s a good question to ask about a thesis or a PhD, but a hard one to answer. There are lots of possible factors.
- How much does your supervisor think you need to do?
- How much time can you spend?
- How many chapters or words are people telling you that need to write?
- How many experiments/interviews/papers/tests/models/observations/questions are you being told that you need to complete?
At the start of a PhD you might struggle to respond to the question of how much is enough. All of these factors, and lots more, could make it tricky to consider.
Nearer the end you can give a response and reasons: “This much, and here’s why.”
And the sooner you decide how much is enough, the sooner you’ll be able to work towards that goal.