I was wondering what the A4 to book size ratio is, say you've written 100 pages on word, how many would that be in a medium sized paperback book?
It depends on so many things, such as font, font size, double, 1,5 or single spacing, margins... It would be easier for you to check the word count and divide that with as many words as you usually find in a page of the books you read. And even in that case it could vary enormously.
that's right... but there's no good reason for you to be considering book size, unless you're going to self-publish it... agents and publishers only want total word count, rounded off to nearest 500 or 1k... and for a first novel by a new and unknown writer, most publishers want a word count of 80-100k... so that's what you should aim for, not the number of pages...
From what I heard, the standard page on a book is 250 words. If you have 80,000 word novel like I do, it would be 300+ page novel. I wouldn't have a book lower then 300+ unless it's a children book.