---
title: "ISBN checker and converter — validate ISBN-10 and ISBN-13"
description: "Check whether an ISBN is valid, convert between ISBN-10 and ISBN-13, and see the registration group it was issued in. Free, no sign-up."
source: https://usegalley.com/resources/isbn-checker
---
[Home](https://usegalley.com/) [Resources](https://usegalley.com/resources) ISBN checker

# ISBN checker and converter

Paste an ISBN. This tells you whether the check digit adds up, converts it between the ten and thirteen digit forms, and names the registration group it was issued in.

ISBN Hyphens and spaces are ignored. An X at the end of a ten digit ISBN is fine.

Verdict

Valid ISBN-13

This runs entirely in your browser. Nothing you type is sent anywhere, and
there is no account to make.

## How an ISBN check digit works

**ISBN-13.** Multiply the first twelve digits alternately by 1
and 3, sum them, and the check digit is the number that brings the total up
to the next multiple of ten. It is the same scheme as every other EAN-13
barcode, which is why an ISBN scans at a till.

**ISBN-10.** Multiply the nine digits by 10 down to 2, sum them,
and the check digit brings the total to a multiple of eleven. Because the
remainder can be ten, the last character is sometimes an X.

**Converting** a 10 to a 13 means dropping the old check digit,
prefixing 978, and working out a new one. Going the other way only works on
a 978 prefix. A 979 ISBN has no ten digit equivalent, because there were no
ten digit numbers left to map it onto.

The registration group is the second element of the number and says which
agency issued it, not where the book was printed. Group 0 and 1 are the
English language agencies, which is why almost every British and American
novel starts 978-0 or 978-1.

An ISBN identifies an edition. Galley keeps one per
[edition and translation](https://usegalley.com/docs/series-and-translations), beside
the manuscript it belongs to, so the paperback and the ebook do not end up
sharing a number.

**For working things out, not for signing anything.** Printers
and retailers set their own rates and specifications, change them without
notice, and none of them is affiliated with me or with Galley.
I checked these figures by hand in August 2026
against [the International ISBN Agency](https://www.isbn-international.org/).
Confirm on the official page before you commit money to a price, a
print run or a contract.

## Questions

How do I check if an ISBN is valid? Every ISBN ends in a check digit worked out from the digits before it. For an ISBN-13 you multiply the first twelve digits alternately by 1 and 3, add them, and the check digit is whatever brings the total to a multiple of ten. If it does not match, the number is wrong somewhere.

What is the difference between ISBN-10 and ISBN-13? ISBN-13 is the ISBN-10 with a 978 prefix and a recalculated check digit, so the two are the same book. Everything issued since 2007 is a 13. Older books still carry a 10 on the copyright page, and library catalogues still ask for it.

Do I need an ISBN to self-publish? Not for a Kindle ebook, which uses Amazon’s own identifier. You do need one for a paperback or hardcover. KDP will give you a free ISBN, but it lists Amazon as the publisher of record and only works for Amazon printing, so buy your own if you want to sell the book anywhere else under your own imprint.

Do I need a separate ISBN for every format? Yes. Paperback, hardcover, ebook and audiobook are four separate products and take four separate ISBNs. A second edition takes another. A reprint with a new cover does not.

## Next

[Front and back matterThe copyright page the ISBN goes on.](https://usegalley.com/resources/front-and-back-matter-checklist) [Amazon description formatterThe rest of the listing.](https://usegalley.com/resources/amazon-book-description-formatter) [KDP royalty calculatorWhat the edition earns.](https://usegalley.com/resources/kdp-royalty-calculator) [ISBN barcode generatorThe valid number, drawn as a scannable EAN-13.](https://usegalley.com/resources/isbn-barcode-generator) [Copyright page generatorWhere the number goes inside the book.](https://usegalley.com/resources/copyright-page-generator)

More at [the resources index](https://usegalley.com/resources).

Put all this into practice when you write your novel in Galley.

[Launch Galley](https://app.usegalley.com)