You should aim to write a thesis of 80000 words. The word limit is exclusive of words in tables, bibliographies, maps and appendices. Footnotes are included as part of the word limit.
Exactly as many as you need to get your committee to sign of on it. (Obviously also to present you work properly.)
Page or word count is not a useful metric for PhD dissertation. This isn’t an undergraduate essay. It’s the culmination of several years research work.
I think that how many papers you’ve published in peer review journals is what you should be worrying about.
Specific details about doctoral dissertations differ according to institutions, departments, and fields of study. In my department, a typical dissertation contains five chapters consisting of an introduction, three data chapters, and an overall conclusion.
Its depends upon university.
For masters – minimum 80 to 100 pages
For PhD – minimum 150 to 400 pages.
Average length of PhD dissertations by major:
One of my colleagues wrote a Book on the assessment of very large strain response of metals to large impact and impulsive loads. That thesis was well over 200 pages.
Indeed, most of the PhD theses in the Aero-Astro department were 200 to 300 pages in length.