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What Is an ISBN? The 13-Digit International Standard Book Number Explained
An ISBN is the unique 13-digit identifier on every published book. Here is what it means, how to get one, and how it differs from KDP's ASIN.
ISBN stands for International Standard Book Number. It is a unique 13-digit commercial identifier issued to every published book edition by national ISBN agencies (Bowker in the US, Nielsen in the UK, the International ISBN Agency globally). Since January 1, 2007, all ISBNs are 13 digits — older books may still display the 10-digit ISBN-10 format.
Each format and edition of a book gets its own ISBN. The paperback, hardcover, audiobook, large-print, and each language translation of the same title need separate ISBNs. Bookstores, libraries, distributors, Amazon, IngramSpark, and most retail catalogs use the ISBN to identify and order specific editions.
How an ISBN is structured
A 13-digit ISBN breaks into 5 parts: (1) Bookland prefix — 978 or 979, identifying it as a book; (2) Registration group — country or language area (0/1 for English-speaking, 2 for French, 3 for German, etc.); (3) Registrant — the publisher; (4) Publication element — specific edition; (5) Check digit — single digit computed mod-10 from the previous 12. Total length is always 13 digits with optional hyphens separating the parts for readability.
ISBN-10 vs ISBN-13
ISBN-10 (10 digits) was the standard before January 1, 2007. ISBN-13 (13 digits) replaced it by adding the 978 Bookland prefix to align ISBNs with the EAN-13 barcode system. Any pre-2007 ISBN-10 has a direct ISBN-13 equivalent: prepend '978' and recalculate the check digit. The 979 prefix was added later to expand capacity. Amazon books published before 2007 may still show ISBN-10 as the ASIN.
How to get an ISBN
In the US: Bowker (myidentifiers.com) sells ISBNs — $125 for a single, $295 for 10, $575 for 100, $1,500 for 1,000. In the UK: Nielsen (£89 single). Other countries: your national ISBN agency listed at isbn-international.org. Amazon KDP offers a FREE ISBN if you publish exclusively through KDP — but that ISBN is locked to KDP distribution. Use Bowker if you want flexibility to publish through IngramSpark, Apple Books, or libraries.
ISBN vs ASIN: which do I need?
ISBN is the global book identifier — used by every bookstore and library worldwide. ASIN is Amazon's internal product code — automatically generated when you create a KDP listing. For Amazon Kindle e-books, ASIN suffices (no ISBN needed). For paperback/hardcover on KDP, you need an ISBN — either Amazon's free one or a purchased Bowker ISBN. For distribution beyond Amazon, you NEED your own Bowker ISBN, not the free KDP one.
FAQ
What is an ISBN used for?
An ISBN is a unique 13-digit identifier for a book. Bookstores, libraries, distributors, and online retailers use it to find, order, and reference the exact edition you want. Each format (paperback, hardcover, audiobook, e-book) and each language translation gets its own ISBN.
How do I get my ISBN number?
Buy from your country's ISBN agency: Bowker (myidentifiers.com) in the US, Nielsen in the UK, or your national agency listed at isbn-international.org. Amazon KDP gives you a free ISBN if you publish exclusively through them — but that ISBN can't be used for IngramSpark or other distributors. For multi-platform distribution, buy from Bowker.
How much does 1 ISBN cost?
Bowker (US): $125 for a single ISBN, $295 for 10, $575 for 100, $1,500 for 1,000. Nielsen (UK): around £89 for a single. KDP's free ISBN: $0 but limited to Amazon exclusive distribution. Generating the barcode image (using our generator above) is always free regardless of where you sourced the ISBN.
Does KDP offer free ISBN?
Yes — Amazon KDP gives a free ISBN if you publish through them. But it's restricted: the KDP-issued ISBN can't be used for IngramSpark, Apple Books, or library distribution. If you ever want to publish beyond Amazon, you need to buy your own ISBN from Bowker — and once a KDP free ISBN is assigned, it can't be transferred.
Is selling 3,000 copies of a book good?
For self-published books, yes — the average self-published digital-only book sells about 250 copies in its lifetime. Hitting 3,000 puts you in roughly the top 5% of indie titles. Traditional bestseller thresholds are much higher (10k+/year for major retailers), but 3,000 is a clear commercial signal that the book has an audience.
What's the difference between ISBN-10 and ISBN-13?
ISBN-10 was the original 10-digit format used before January 1, 2007. ISBN-13 (13 digits) replaced it to align with EAN-13 barcodes — every pre-2007 ISBN-10 has a corresponding ISBN-13 with '978' prepended. New ISBNs since 2007 are always issued as ISBN-13.
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