As stated in the Student Registry PhD format requirements, a PhD thesis in the Department of Computer Science and Technology “is not to exceed [...] 60,000 words including tables and footnotes, but excluding appendices, bibliography, photographs and diagrams.”
Candidates abusing these rules mostly risk annoying their examiners. Of particular concern is the misconception that tables and equations do not count as words, while they actually take significantly longer to read than mere text. The words “photographs and diagrams” refer to entities that can be taken in with a single glance rather than a page of detailed equations. Tables, equations and the like are best counted as having the number of words that text occupying the same area would have. The safest way to justify being under the 60,000 word limit is to count the words on a page with most plain text, and divide 60,000 by that to give a page limit. Another way of getting an estimate of the effective word count is
$ ps2ascii thesis.pdf | wc -w
If the main body of your thesis (from first page to last page before the bibliography) is 150 pages or more then you have probably exceeded the size limit – and your thesis risks summary rejection. Remember that it is not necessary to write 59,995 words; as noted in the regulations for Physics and Chemistry: “[the] Degree committee points out that some of the best dissertations extend to only half this length”.
Sometimes candidates would like a bigger word-count limit. This is often a sign they have done too much work; a good thesis selects from the work done rather than slavishly including every minor result. There are three reasons not to do too much work on a thesis: poverty after your funding expires, scoring black marks for the department by submitting four years after starting, and having to leave out research results from your thesis!
Addendum:
The Degree Committee for the Faculty of Computer Science and Technology agreed, at its meeting of July 2nd 2009, that the word limit will remain at 60,000 words and, furthermore, emphasized that should students exceed 175 pages, students and their supervisors will be asked to explain.
The Degree Committee for the Faculty of Computer Science and Technology agreed, at its meeting on 23 November 2021, that while the word limit will remain at 60,000 words, the Committee recognises some theses are interdisciplinary. An application for an extension to the word counts where there is a compelling case - such as an interdiscipinary thesis - will be considered. Students should apply for an extension to the thesis word count via CamSIS Change of Circumstances.