Most students run out of words when writing up. At the start of the process, especially if you're an undergraduate doing a dissertation for the first time, 10,000, 12,000, or 15,000 words (and up) sound like a lot, but they soon get eaten up. Worst still, they get eaten up in the wrong places, so you have a lop-sided dissertation, with some chapters receiving more focus than they should, whilst others are relatively neglected. Your dissertation guidelines might provide some instructions or recommendations on word count per chapter, but this is not always the case. Since you're likely to run out of words at some point during the writing up process, we'd recommend the following:
Always leave extra words for your Results chapter. This chapter can be concisely written, especially when you know how to summarize data well and make good use of Appendices. However, more often than not, too much is included and it becomes excessively large. The problem is that you can suddenly find the Results chapter becoming 1,000 to 2,000 words too long (sometimes more), and it's very hard to either shorten the chapter or reduce the word count in other chapters. Leaving a little extra in terms of word count for this chapter is advisable, but when it comes down to it, knowing how to write up the Results chapter properly is important and will help you get this right first time.
Don't waste words on peripheral sections within chapters. Every chapter has a number of sections that are useful, and often have to be included to some extent, but (a) can eat into your word count and (b) won't give you lots of extra marks by themselves. Obvious examples include the Chapter Summaries section within the Introduction chapter, as well as necessary components such as Acknowledgements. In the case of Acknowledgements, this is sometimes even included in your word count, despite having no influence on the mark you are awarded, even though you would be expected to include it.
Don't waste words (a) waffling or (b) going off-point in your Literature Review, Research Strategy and Results chapters. Now there is a difference between waffling and going off-point:
Going off-point
When writing a dissertation as a student, as opposed to a conference paper or journal as an academic, you have to provide a lot more explanation of possible choices you could have made, rather than simply justifying the choices you made. For example, in the Research Strategy chapter, you'll often be expected to explain the differences between research designs, research methods or sampling strategies that could have been used. This is sometimes the result of a marker needing to know that you have read up about the available options and can demonstrate this by briefly summarising these different components of research strategy. This is what we mean by going off-point, and it can be a real word hog, eating into your available word count. You need to try and avoid this by keeping these sections short, but also focusing on justifications (i.e., why you are using one research method or sampling strategy over another), which when written well, demonstrate your understanding of different components of research strategy, without having to waste words explaining each component in turn.
Waffling
Ignoring waffling that comes from laziness - we know this happens! - waffling is often a problem of the Literature Review and Results chapters. Waffling is simply similar to dumping everything you know on the page, which can happen when (a) you don't know the material very well or (b) you're struggling to gauge which content is important and which can be left out, something that is a real challenge for the first-time dissertation student. As a result, you add too much content. This happens a lot in the Literature Review chapter because it is hard to be selective and critical, and in the Results chapter when you don't know (a) what analysis should be included, (b) what can be omitted entirely, and (c) what can be removed and put into the Appendix. In these chapters within the Route #1: Chapter-by-Chapter section of Lærd Dissertation, we help you to avoid this kind of waffling, which not only saves words, but makes your argument much more coherent.
Finally, there can be an obsession with word count when doing marked work. You're doing an essay of 1,500 words or 3,000 words, and you try to use every single word available. This can make sense when you have a small word count and lots of worthwhile things to say in such a small space. However, when taking on a much larger document (i.e., 10,000 words or more), it is not only important what is being said, but also what you leave out. Rather than thinking too hard about word count, focus on making sure that everything being said is worthwhile. All chapters, but especially your Literature Review and Results chapter can lose a lot of quality simply because of three or four unnecessary paragraphs that disrupt the flow and logic of your arguments and results. Despite the added word count of dissertations compared with essays, less can be more.