There is not a minimum length or page count that we mandate for books, nor a minimum word count. As far as we are concerned, conciseness is a virtue when compared with waffling on for page after page with turgid prose.
However, we realise that most readers prefer to hold in their hands a book of at least a reasonable length, and that books may feel “too short” for the amount of money paid. Conversely, books can easily be “too long”, becoming large and awkwardly sized, and costing a fortune to print, resulting in an exorbitantly high RRP for readers.
Therefore, finding a middle ground is probably the best policy. We would generally recommend aiming for between 150 and 280 pages. A short book is perfectly fine if your written language is exceptionally well-constructed and there is no waffling. A long book is also perfectly fine if there is a lot of material to be written, but waffling and a poor quality of written language will not be acceptable. Books outwith this range may be considered, but you should aim for this range if at all possible.
A word count is virtually meaningless, since different numbers of words will fit on different sizes of pages. A book published in A4 size will have many more words per page than an A5 publication, and both of these will have a different number of words per page than a book published in crown quarto. Furthermore, choice of font and text size will affect the number of words per page. If you absolutely must have a guideline for word count, then 150-280 pages for a US trade (a fairly average) sized publication could be around 50,000 to 70,000 words.
However, a 70,000 word manuscript with only 40,000 good words is going to be cut down to those 40,000 words in editing, so it is probably better in the long run if you just focus on writing well, being concise, and producing a good quality manuscript of roughly 150-280 pages in whatever book size you imagine will be most suitable for your work. If you don’t know what dimensions would best suit your work, then just aim for 120-150 pages A4, and discuss the matter with your editor.