How many words does a book usually have?

The length of the book depends on many factors such as the theme, difficulty, style, and the author's experience level. Generally speaking, the book should be readable and professional, and it should contain enough content to support the requirements of the title. If the subject of the book was broad, it might need to cover many aspects such as professional skills, academic works, novels, etc. The length of the book would be different. If the subject of the book was more in-depth, such as academic papers, professional reports, etc., the length of the book might be longer. The length of the book should be within an appropriate range to ensure that the content of the book is complete, rich, easy to understand, and can meet the requirements of the title. The specific length of the book still needed to be evaluated and decided according to the specific situation.