An ASIN is Amazon’s own catalogue number, and Amazon creates one automatically for every product it lists, including every book. An ISBN is the book trade’s number, and it may come from an ISBN agency or the platform through which you publish. The ASIN vs ISBN question matters because a print book on Amazon carries both, and only one of them works anywhere else.
ASIN vs ISBN: What Is Each Number For?
ASIN stands for Amazon Standard Identification Number. It is a 10-character code, and Amazon gives one to every item in its store: a kettle, a pair of shoes, or your paperback. You never apply for one. Amazon attaches it to the listing rather than to the book, so it appears when your title goes on sale.
An ISBN is the International Standard Book Number, and it belongs to the whole book trade rather than to one shop. The International ISBN Agency has issued 13-digit ISBNs since 1 January 2007, and every one of them starts with 978 or 979. Publishers, booksellers, libraries and internet retailers all use it for ordering, listing and stock control. You can buy one from the ISBN agency for your country, or take a free one from the platform you publish through.
So the difference is reach. An ASIN works inside Amazon, while an ISBN travels the whole supply chain: every wholesaler, shop and library that handles books. There is a second difference authors run into before that one: the ISBN goes inside the book itself, and the ASIN never appears in it at all.
Where the ISBN Appears in a Printed Book
The ISBN appears in two places on a finished print book. We set it on the copyright page, the page near the front that records the edition, the publisher and the copyright notice. We also encode it in the barcode printed on the back cover, which is the striped block that lets a scanner read the ISBN instead of someone typing it out. Neither of those can hold an ASIN, because the ASIN belongs to Amazon’s listing rather than to the edition.
Why Does a Paperback’s ASIN Sometimes Look Like an ISBN?
Every ASIN is 10 characters long, but they do not all look alike. Some are a plain run of digits, and some mix letters and digits. On books that difference is not random, because it traces back to the ISBN the book already carries.
ISBNs moved to 13 digits on 1 January 2007, and the first of them all began 978. That supply was finite. IngramSpark’s guide to 979 ISBNs records that in 2019 “Bowker, the United States ISBN Agency, announced plans to use a new prefix, 979, due to diminishing inventory of 978-ISBNs”. Both prefixes are in use today, and the gap between them is what decides your ASIN.
A 978 ISBN has an equivalent 10-digit version, because that prefix was built to stay compatible with the numbering system in use before 2007. The short version is the ISBN-10, and Amazon uses it as the ASIN. A 979 ISBN has no such version, because the prefix “is not backwards-compatible and cannot be converted into an ISBN-10 counterpart”. With nothing to reuse, Amazon generates a code of its own, which is why those books carry an ASIN beginning with a B.
That also explains something you may have noticed while looking at your own book. A product details block often shows one of the two codes rather than both, because on a 978 book they are the same number wearing different labels. The web address is the dependable place to look: whatever follows /dp/ is the ASIN.
Two real listings show the ASIN vs ISBN relationship in each of the two cases:
| Paperback | ISBN-13 | ISBN-10 | ASIN |
|---|---|---|---|
| Becoming | 978-1524763138 | 1524763136 | 1524763136, the ISBN-10 reused |
| Anatomy and Physiology 2e | 979-8848230314 | none | B0BCSBGL5D, generated by Amazon |
Wondering why the last digit changes between the ISBN-13 and the ISBN-10? Our explainer on ISBN-10 vs ISBN-13 works through it. None of it changes the files we build, in any case: we generate the cover barcode from the ISBN-13, and a 979 ISBN encodes exactly as a 978 one does.
Which Number Do You Need, and Who Asks for It?
Print formats need ISBNs. A Kindle ebook does not need an ISBN, but you can assign one that you have bought yourself. Which number you quote afterwards depends on who is asking. Start with the ISBN side. The International ISBN Agency’s rule is that “each different product form (e.g. paperback, EPUB, .pdf) should be identified separately”. Those are examples rather than the full list. A hardcover is a different product form from a paperback, so it needs its own ISBN as well. KDP’s help page What is an ISBN and Imprint? says so directly: “Each format of your book (paperback vs hardcover) needs its own ISBN”. It adds that the same ISBN cannot be reused across formats, or across a new edition with significant changes.
Do Kindle Ebooks Need an ISBN?
Ebooks are the case where KDP’s own pages disagree, so it is worth pausing here before you buy anything. The ISBN page above says ebooks are among the formats “where an ISBN is optional”. KDP’s Create a Book page says something else: “You will need a unique ISBN for each format of your book: eBook, paperback, and hardcover.” Both sentences were live on 18 August 2026.
The setup screen settles it. When you upload a Kindle ebook, the field is headed “ISBN (Optional)” and tells you that “Kindle eBooks are not required to have an ISBN”, and the book publishes with the box left empty. KDP’s free ISBNs point the same way, because they cover print formats only. You can still fill the box in if you own an ISBN and want the ebook traceable through the wider book trade. Nothing obliges you to.
Which number you quote depends on who is asking. Anyone outside Amazon works from the ISBN: a bookshop ordering stock, a library cataloguing a copy, or a distributor listing you beyond KDP. Inside Amazon, the ASIN identifies the listing, which is why Amazon’s own tools ask for it.
Publish a Kindle ebook and nothing else, and the ASIN can be the only number your book ever has. That is not a gap to worry about. Nothing in an ebook we deliver for Kindle carries an identifier at all unless you have purchased your own ISBN; the ASIN arrives once the file is uploaded.
The ASIN vs ISBN distinction comes down to this: an ASIN is Amazon’s shelf label, and an ISBN is the book’s passport. If you are publishing in print, settle the ISBN before the cover goes to design, because the barcode has to carry it. If you are publishing a Kindle ebook and nothing else, you can let Amazon do the numbering and spend the money elsewhere.
Further Reading on Book Identifiers
ISBNs come with a lot of small, separate questions, so we have worked through most of them one at a time:
- ISBN-10 vs ISBN-13: what the two formats are, and whether you still need to know your ISBN-10.
- Free ISBNs: what you give up when a platform supplies the number instead of you.
- Separate ISBNs for KDP and IngramSpark: whether one paperback can carry one number across both.
- ISBNs and barcodes: whether you have to buy the barcode as well as the number.
- The EAN-5 add-on: the second, smaller barcode beside the main one, and when it earns its place.
- Audiobook ISBNs: when an audiobook needs its own number and when it does not.
- Revised editions: how much has to change before the book needs a fresh ISBN.
- Updating a published book: what changes on an Amazon listing once the book is already live.
Frequently Asked Questions
Is an ASIN the same as an ISBN?
An ASIN and an ISBN are separate systems that happen to overlap on print books. Amazon issues the ASIN, and it only means something inside Amazon. An ISBN agency issues the ISBN, and bookshops, libraries and retailers everywhere recognise it. A print book on Amazon carries both at once.
My print book already has an ISBN. Why has Amazon given it an ASIN as well?
Amazon gives an ASIN to everything in its store, whether or not the item already carries an industry number. The ASIN identifies your listing in Amazon’s catalogue, and the ISBN identifies your edition in the book trade. Neither one replaces the other, so having both is normal.
Where do I find my book’s ASIN?
The web address is the surest place: whatever follows /dp/ on the book’s Amazon page is the ASIN. For your own titles, KDP’s guidance on linking to your book says it also sits “under the book’s title in your KDP Bookshelf”, which is the list of your titles inside your KDP account, “or on the book’s detail page under ‘Product Details'”. Expect that last one to be hit and miss on print books, because a 978 title often shows its ISBN-10 there instead, and the two are the same number.
Does an audiobook have an ASIN or an ISBN?
An Audible audiobook has its own ASIN, separate from the ebook’s, because Audible is Amazon’s audiobook company and the same numbering runs through it. ACX’s help on claiming a title asks for the ebook’s ASIN before production starts. It also explains that the audiobook’s own ASIN begins B0 and can be read out of the Audible web address. Whether the audiobook needs an ISBN as well depends on where else you sell it, which we cover in our post on separate ISBNs for audiobooks.
Do the paperback and hardcover of my book share an ASIN?
A paperback and a hardcover are two products, so they get two ASINs, and KDP requires a separate ISBN for each of them as well. Amazon often links the two on one shopping page so readers can switch between them. The underlying listings and their numbers still stay separate.
