How many spells can a spellbook hold? It's unrealistic to think that a spellbook could contain an unlimited number of spells!

According to the Third Edition Player's Handbook, a spellbook is 100 pages and can hold a spell level for every two pages. This means that one book can hold up to 50 levels of spells, that means that it can hold:

50 Cantrips
50 First Level Spells
25 Second Level Spells
16 Third Level Spells
12 Fourth Level Spells
10 Fifth Level Spells
7 Seventh Level Spells
6 Eighth Level Spells
5 Ninth Level Spells

Back in the day, we would refer to the Unearthed Arcana (1985 AD&D by Gary Gygax). It says that you could write up to 8 ninth level spells in a standard book and 2 in a travelling book. It goes on and breaks that down into a simple number per level of spells. But that's not good enough for me.

According to the Unearthed Arcana, Boccob's Blessed Book could contain up to 45 levels of spells. If you tally up regular spell books in the same way, a standard book could contain 72 levels of spells (8 ninth level spells) and Traveling book could contain 18 levels of spells (2 ninth level spells). That figures out to be this:

Standard book
72 Cantrips
72 First Level Spells
36 Second Level Spells
24 Third Level Spells
18 Fourth Level Spells
14 Fifth Level Spells
12 Sixth Level Spells
10 Seventh Level Spells
9 Eighth Level Spells
8 Ninth Level Spells

Traveling book (two ninth-level spells = 18 spell levels)
18 Cantrips
18 First Level Spells
9 Second Level Spells
6 Third Level Spells
4 Fourth Level Spells
3 Fifth Level Spells
2 Seventh, Eighth, or Ninth Level Spells

First Edition Equipment

Item	Cost	Weight
Standard Spellbook	15 g.p.	43
Travelling Spellbook	5 g.p.	11

Second Edition Equipment

Item	Cost	Weight
Standard Spellbook	15 g.p.	3 lbs.
Travelling Spellbook	5 g.p.	1 lbs.