I have been reading the Dunleavy authoring a Phd book (I am currently writing chapters/organising bits and pieces of what I have wrote before etc) and I have found that chapters should be around 10,000 words each and never less than 6000 words. What I have written to date is mainly in 3500-6000 words (1 chapter...the background and state of knowledge is 9000 words, because I am joining two areas and need to give quite a lot of background, my methods is around 3000 words, intro chapter is about 1000 words). I should also have 8 chapters in all (Intro, Lit Review, Methods, 3 results & discussion, 1 discussion, 1 conclusion) I am doing my PhD in environmental/analytical chemistry.

Anybody have any advice about how long a chapter should be, and whether this should be acceptable?

Although you will often see advice to keep chapters around 10,000 words, try and keep them all roughly the same length, etc., every PhD is different. In subjects such as the humanities, it may make more sense to try and stick to a more set structure, as the PhD is more like a story and flow is very important. However, a science PhD is very different, as the chapters are often individual sections describing different experiments. Therefore, it is difficult to 'force' them to be a certain length.

My PhD was in pharmaceutical science, and the structure was very similar to yours. My intro was about 10,000, followed by four result chapters of 10,000, 7,000, 6,000 and 12,000 words. My discussion/conclusions chapter then came to about 8,000. If I were you, I'd try not to worry too much about the length, as long as the overall thesis isn't massively long or obviously short, then it will be fine! If you feel you've covered each section in enough depth then that is all that matters.