The most widely accepted answer to how long should a dissertation literature review be is roughly 20 to 30 percent of your total word count — so around 2,000 to 3,000 words for a 10,000 word dissertation and between 3,000 and 6,000 words at masters level. always verify with your module handbook first because your institution's own guidelines will always be more precise than anything you find online.
what matters far more than the number though is whether your how long should a dissertation literature review be target is filled with genuinely critical writing that engages with key debates, identifies gaps in existing research, and builds a convincing case for your own research question — because that is what actually determines your grade.