- A 13-digit unique identifier per book format.
- One ISBN per format (paperback, hardcover, ebook, audiobook).
- U.S. agency: Bowker.
- Costs: ~$125 each, or ~$295 for ten, or ~$575 for a hundred.
- Free through KDP for Amazon-only ebooks (but the ISBN belongs to Amazon).
An ISBN (International Standard Book Number) is a 13-digit unique identifier assigned to each format of a book — separate ISBNs for paperback, hardcover, ebook, and audiobook. The U.S. agency is Bowker; ISBNs cost about $125 each (or ~$295 for ten) or are free through KDP for Amazon-only ebooks. Required for print; optional for KDP-only ebooks.
Chapter i·Why it matters
ISBNs are how the industry tracks books. Owning your own ISBN means owning your book’s identity across retailers; using KDP’s free ISBN means Amazon owns the ID. For indie authors planning to distribute beyond Amazon, owning ISBNs is non-negotiable.
Chapter ii·What to include
- One ISBN per format you publish.
- A Bowker account (or local country agency).
- A budget: ~$295 for ten ISBNs (covers ~3 books in all formats).
- Buy ISBNs in batches of 10 — much cheaper per unit.
- An ISBN log: book title, format, ISBN, date assigned.
- A "you own it" check: free ISBNs from KDP are NOT owned by you.
Chapter iii·Example
A self-publishing author buys ten ISBNs from Bowker for $295. She uses three for her current book (paperback, hardcover, ebook), one for her audiobook later. The remaining six cover her next book and a half. Total per-book cost: ~$70 instead of $500 buying singly.
Chapter iv·Related questions
In WriteLoom
See your book the way a browsing reader will
WriteLoom’s Sell studio tracks ISBNs per format alongside the rest of your metadata.
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