This is a question long debated by writers, publishers, and agents: How long should a book be?
Personally, I think it depends on several different factors. See if you agree or disagree with me.
1. Genre: Fantasy is allowed to be a lot longer than a contemporary romance, for instance. My newest release Bait is Urban Fantasy and clocked in at 123,000 words. WHAT??? I know. It's long, but it had to be that long for the story to be told. So many thing happen. If I'd tried to tell the story in my usual 80,000 words, people would have been complaining they felt like they'd been hit by a train afterwards. There wouldn't be time for a reader to relax and get to know the characters between all that action.
2. Publisher: The book length also depends on where you want to publish it. If you want to keep complete control like me and do it yourself, you can write it as long as the story needs to be. If you want to go traditional, you need to find out what the publishers are looking for and give it to them.
3. The Story: How long do you need to tell the story well? If you make it too short, readers will feel cheated. If it is too long, you risk losing their interest.
There are probably other factors to consider, but I can't think of any at the moment.
Can you? If you can, please use the comment section and let us know. Thank you.