@JeremyECrawford How many pages does a spell take up in a spellbook? Can't find it in the books.
— Jarred Caldwell (@jarred_caldwell) April 27, 2016
There's no rule for the number of pages a spell takes up in a spellbook. Up to you and your DM. #DnD https://t.co/9fFrxZZIQj
— Jeremy Crawford (@JeremyECrawford) May 3, 2016
I assume the time of casting plays a part, so an action being 6 seconds limits the length of the spell but that preparatory information, use warning and such might have such a spell be a page per level. a spell that takes longer to cast would have more ancillary text.