How many pages do spells take up in the wizards spell book?

@JeremyECrawford Hej, I ran into a problem. How many pages do spells take up in the wizards spell book? I can't find it in the PHB.

— Yorik Modder (@Pandab13r) December 8, 2016

There's no rule for how many pages a spell takes up in a spellbook. Common house rule: 1 page/spell level, so 9 pgs. for 9th lvl spell #DnD https://t.co/chFmQVexyc

— Jeremy Crawford (@JeremyECrawford) December 8, 2016

@Pandab13r i believe it is one page per spell level #wotcstaff

— (((Mike Mearls))) (@mikemearls) December 8, 2016