The honest answer is that length is a consequence, not a target. But authors ask, and vague answers help nobody, so here are the numbers we actually work to.
Monographs: 80,000 to 140,000 words
Below eighty thousand a research monograph usually reads as an extended article that has been padded. Above one hundred and forty thousand, the production cost rises steeply and libraries start balking at the price point. Most of our research titles land between ninety and a hundred and ten thousand.
Course texts: 60,000 to 110,000
Constrained by the semester, not by the subject. A text that cannot be taught in twelve weeks will not be adopted, however good it is.
Edited volumes: ten to sixteen chapters
Fewer than ten and the collection looks thin on a library catalogue. More than sixteen and the editorial burden of chasing contributors becomes the dominant cost of the project.
When to break the rule
Reference works and annually updated legal titles follow entirely different logic. If your book is one of those, ignore everything above and talk to your editor.
