I guess that is one of those question that, like how long is a piece of string, has no real answer, yet is a question many starting authors ask themselves. At least I know I have.
Looking around, the answer varies depending on who you ask. Some say 60-100,000 words, others 100-150,000. It also does vary between author and genre. Some tend to the shorter, while others, most especially fantasy, tend to the epic (in the truest sense of the word), clocking in at quarter of a million words or more, large enough to bludgeon someone to death with. Oft times a story could be told in 100,000 words yet still weigh in at 250,000, in book after book, reduced to a turgidity of shallow, endless characters and plots that no longer make sense, and the only reason they see light of day is to cash in on a name or because of contractual obligations (which, ironically, was the name of a Monty Python album), and should be allowed to die peacefully, but continue on and on, rather like this sentence.
For myself, I am often guilty of over planning things, to the point that they interfere in the doing of the plans. I like to work to a set target, of a set number of chapters. I have always had in mind a target of a prologue (though that is falling from favour) and twenty one chapters, each of around 3-5,000 words, preferably 4000, the chapters split into three parts, the start of the story, the middle of the story and the end of the story. A lot of advice I have seen is not to worry so much about the length, but just write until the story is done. My mind really doesn’t work that way. Hopefully that screwy brain-wiring won’t cause problems for me.
Mist and Shadows 