What is the difference between ISBN-10 and ISBN-13?

Quick answer. ISBN-10 and ISBN-13 are the same identifier in two lengths. A 10-digit ISBN was the standard from the 1970s until 2007; a 13-digit ISBN has been the standard for every new book since 1 January 2007. The number grew from ten digits to thirteen so it matches the 13-digit EAN-13 numbering the rest of retail already uses. If you are publishing a new book today, you will be assigned a 13-digit ISBN. Any old ISBN-10 converts to its ISBN-13 form by adding a 978 prefix and recalculating the final check digit; the book keeps one identity, only written one way.

Do not confuse the two lengths with "two ISBNs per book". These are two lengths of the same number, not two different numbers. What genuinely multiplies your ISBN count is format: paperback, hardcover and eBook each need their own (see how much an ISBN costs).

Key takeaways

• ISBN-10 = the old length (pre-2007). ISBN-13 = the current length (2007 onward). Same concept, different digit count.
• Every new ISBN issued today is 13 digits. You do not choose; that is what your national agency issues.
• The reason for the change was compatibility. ISBN-13 is written in the same 13-digit EAN-13 form retailers already use, and it opens up far more numbers.
• An ISBN-10 converts, it does not disappear. Add 978, drop the old check digit, recalculate — the same book, now 13 digits.
• A book does not need both. One edition carries one ISBN; it is simply written in the current 13-digit form.
• A 979 prefix has no 10-digit ancestor. Only 978-prefixed ISBN-13s convert back to an ISBN-10. 979 was added later and never existed in 10 digits.
• The format rule still rules. Length is separate from the format question: each format still needs its own number.

ISBN-10 vs ISBN-13 side by side

The important row is the last two: old ISBN-10s are not invalid — a book published in 1999 still carries the number it was issued. It simply is not the length used for anything new.

Why the number changed at all

The move from 10 to 13 digits was not a cosmetic upgrade. Retail scans EAN-13 barcodes for everything on the shelf, and a 10-digit book number had to be converted into that form to be scanned. Making the ISBN itself 13 digits removed that step.

Two things follow:

1. One numbering system — the book sits in the same product-number family as other retail goods.
2. More numbers available — 13 digits leaves room for many more publishers and titles than 10 did.

That is why the 978 (and later 979) prefix appears on the front of every ISBN-13: it is the Bookland prefix, telling an ordinary scanner that the 13-digit number is a book.

How an ISBN-10 converts to an ISBN-13

The conversion is mechanical, and it is worth understanding because it explains why one book never needs "both numbers":

1. Keep the first nine digits of the ISBN-10.
2. Add the 978 prefix in front of them.
3. Discard the old check digit (the tenth character — either 0–9 or X).
4. Recalculate the check digit for the new 13-digit string, using the ISBN-13 formula (alternating weights of 1 and 3).
5. Result: the ISBN-13 for the same book.

One book, one identity: 1-234-56789-X (ISBN-10) and 978-1-234-56789-7 (its ISBN-13) are the same edition written two ways.

The check digit, and why a typo always fails

Both lengths end in a check digit — a value calculated from the digits before it. The system’s point is simple: if one digit is mistyped, the arithmetic no longer balances and the number is rejected before the order goes wrong.

This is why an ISBN copied by hand with a single wrong digit is not a slightly-wrong number — it is a non-number, and a retailer's system will refuse it.

What this means when you publish

• You do not pick a length. Your national ISBN agency (Bowker in the US, and equivalents elsewhere) issues current 13-digit ISBNs.
• If the book already exists under an ISBN-10, you do not need a replacement: the same number is written in its 13-digit form where a system asks for it.
• A 979 ISBN has no ISBN-10 form. It never existed in ten digits, so there is nothing to convert; this is correct, not an error.
• Length is independent of format. Knowing "13 digits" tells you nothing about how many ISBNs a book needs — that is decided by how many formats you sell.

A short check before you publish

1. Confirm which ISBN the edition carries — expect 13 digits for anything new.
2. Do not convert a 10-digit number by hand if you can copy the 13-digit form from the book's existing record.
3. Copy the number; never retype it, so the check digit survives.
4. One ISBN per format, whatever the length — a print ISBN does not cover the eBook.
5. Keep a register of each ISBN, its edition and its format.

If managing ISBNs and format decisions is not how you want to spend your time, it is part of what we handle: our self-publishing packages include ISBN assignment, barcodes, print and eBook setup and distribution.

Frequently asked questions

Do I need both an ISBN-10 and an ISBN-13? No. One edition carries one ISBN. For anything new it is the 13-digit form; older books keep the 10-digit number they were issued, and it converts to 13 digits when needed.

Can I still buy an ISBN-10? No. New ISBNs have been 13 digits since 1 January 2007.

Does an ISBN-13 always start with 978? No. It starts with 978 or 979. Only the 978 numbers have a 10-digit equivalent.

Related guides

Keep going: how to write a book, the types of book editing, book editing services and proofreading services. For a dictionary definition, see ISBN (Cambridge Dictionary).

Disclosure: Harmony Publishing is a self-publishing company and links to its own services where they match a step. The language guidance here is practical, not a rule for every style guide.