Looking back at some of the comments people have made and looking at my plans for the rest of the month, this is post which is probably the most difficult to write in a balanced way. In case it’s not obvious, I’m approaching this from an Engineering/Science background, but I’ve done my best to give advice that is generally applicable, whatever the flavour of your research. In this, clearly I’ve been more successful in some posts than in others! A few coming up will be purely for the Engineers and Scientists out there: I hope the Arts readers won’t hold this against me.
It is a truth universally accepted that Arts theses are substantially longer than (most of) those produced by the sciences. I will not succumb to Arts-bashing, but rather I will put forward the hypothesis that the Arts have to say more because they usually cannot summarise their research in figures and tables.
That said, in reality, there are researchers in both camps who are economic with their phrasing, and are able to present an intelligible argument in very few words. There are others who are prone to florid descriptions and who seem to require 20 words when five would suffice. Still further complicating matters are those who cannot seem to walk into their office without generating data to be analysed and so gather enough for two or three doctorates, whereas there are those who scrabble to get enough material in more time.
As your thesis is not weighed, it makes a great deal of sense to make sure that your thesis is no longer than it needs to be to give the necessary support to your hypothesis, although this does not mean that you should deny yourself the opportunity to put forward your view point on relevant issues. Rather, you should avoid pontificating for the sake of it and, as I have said several times already, you should avoid waffling.
The most important thing to remember is that every thesis is similar, and every thesis is different – almost by definition, unique. On this basis then, it would be foolhardy to prescribe absolute limits on the length that a thesis should be. That said, 200 pages (from the first page of the Introduction to the last page of the Concluding Remarks) is quite a nice number. It has a certain feel to it which is neither too light, nor too heavy. 150 pages should be considered an absolute minimum in order to present a research question and adequately defend it. Anything more than 300 pages feels too much. Note, I do not include any appendices that might be relevant in these page limits. Further, I’m not suggesting that anything outside of this range is wrong, but as a supervisor or examiner I would be factoring this into my assessment.
In C and I (Concluding Remarks and Introduction), I suggested the idea of a page ‘budget’ that you should set yourself. If we allow 10 pages for these two chapters – and this would be about right for any length of thesis – then this allows of the order of 140-290 pages for the bulk. At a minimum this would be three chapters of about 47 pages in length (if you subscribe to the theory that all chapters should be of about the same length. If you have a very focussed project then this might be right: the Literature Review might be a touch shorter, as might the Experimental Methods or equivalent, and the Results and Discussion a touch longer, or you might split this into two chapters. Increasing length is likely to arise from the need to add different techniques (experimental and/or data analytical): individual chapters will likely decrease slightly in length.
My original plan had been to suggest actual page-budgets for typical chapters, but on reflection, I think this would not be as helpful as I first thought. Instead, I would suggest looking at typical documents in your discipline and getting a feel for the typical length that might be expected. I would then look to see if the general structure was one that I wanted to follow, especially with regard to the break down the results and discussion elements. Having determined a rough number of pages and a rough chapter plan, I would then divvy up the pages as appropriate, and take away 10% from each chapter. Having written a given chapter, if I was at or over this limit, up to the length originally determined, I wouldn’t worry too much (except for E for Editing). If I was below this 90% limit or over the 100% page-count, I would have a good hard look at what I had written (taking into account Groundhog Day).
Any thesis should be a pleasure, not a chore, to read, even to the non-expert. This requires clear, concise writing, which explains the problem and the route to solving it. The non-expert might not be able to follow all of the technical points along the way, but the shape of the work should be obvious.