How many pages does a book need to be to be considered long in your opinion?
Opinions vary, but there is one hard line people actually use: word count, not pages, since page counts swing a lot with font and trim size.
The Hugo Awards define a novel as 40,000+ words, a novella as 17,500 to 40,000, a novelette as 7,500 to 17,500, and a short story as under 7,500. https://www.thehugoawards.org/hugo-categories/
At a rough 250 to 300 words per printed page, 40,000 words is only about 130 to 160 pages, so that's "a full book", not "long". The 500-page answers here land around 125k to 150k words, which is roughly three times the novel minimum. That's where most readers start calling it a long book.
The Hugo Awards define a novel as 40,000+ words, a novella as 17,500 to 40,000, a novelette as 7,500 to 17,500, and a short story as under 7,500. https://www.thehugoawards.org/hugo-categories/
At a rough 250 to 300 words per printed page, 40,000 words is only about 130 to 160 pages, so that's "a full book", not "long". The 500-page answers here land around 125k to 150k words, which is roughly three times the novel minimum. That's where most readers start calling it a long book.