What length should a good book be?
Well it depends what you mean by a 'good' book.
If you mean a novel: a novel in Silhouette Books Romance line must run from 53,000 to 58,000 words.
A novel in Silhouette’s Special Edition line must run from 75,000 to 80,000 words.
a historical romance may run from 100,000 to 125,000 words. It depends what your book is.
A good book does not rely on the lenth, it's the old phrase 'Quality over Quantity', it relys on the style of the writing. Publishers wont not publish you because its not that long.
It sometimes depends on the audience.
For young children it is better to have it as short as possible with easy words and more pictures.
For teenagers it can range, a 200 page book is fine for short reading, but they usually preter it to be between 300 and 800 pages.
Adults tend to like long novels and books.
Look at you book and see who it's directed at.
I hope this helps, keep writing and tell me if you have any more difficulties!