I’ve been asked a writer question: Many writers obsess over word count because publishers require a specific number of words for manuscripts so they can plan for a specific number of pages to be printed and figure the costs involved to be sure they don’t lose money.
A short story normally is approximately 4,000 words, though they may occasionally be less and may run as high as 10,000 words. Depends on the publisher and how much space they wish to allocate to each story.
A novella is normally 10,000 to 40,000 words.
A short novel, such as the typical mystery, western, or romance, is 40,000 to 60,000 words.
A long novel is more than 60,000 words and can go as high as the publisher will allow.
If a writer comes in with the wrong word count and wants to be published by a publisher, their manuscript will be rejected without being read.
If the writer, on the other hand, plans on self-publishing, then word count becomes irrelevant except for the convenience of readers who have come to expect the usual word count for whatever type of story they are buying.
I don’t know the specific word counts for non-fiction but I’m fairly certain that they exist.