ISBN checker
This ISBN checker tests the check digit on any ISBN-10 or ISBN-13, converts one form to the other, and shows the number hyphenated when it can. A number is valid when its last digit agrees with the digits before it. 978-0-306-40615-7 passes, and with the last digit changed to 0 the tool says the check digit should be 7.
It checks the arithmetic only. It can't tell you who owns a number or which book it belongs to.
How to use the ISBN checker
Hyphens and spaces are ignored.
Green means the check digit agrees, and red says what it should have been.
Barcodes and retailer uploads use that one.
It reads the first 200.
How the ISBN checker works
The International ISBN Agency's page on how the ISBN is structured describes the check digit as "a Modulus 10 system with alternate weights of 1 and 3."
The ISBN-13 check digit
Multiply the first twelve digits by 1, 3, 1, 3 and so on and add the products. The check digit is 10 minus the remainder after dividing by 10, or 0 if the remainder is 0. For 978030640615 the products add to 93 (9, 21, 8, 0, 3, 0, 6, 12, 0, 18, 1 and 15). The remainder is 3, and 10 minus 3 is 7, giving 978-0-306-40615-7.
The ISBN-10 check digit
Multiply the first nine digits by 10, 9, 8 down to 2 and add them. The check digit is 11 minus the remainder after dividing by 11, and a result of 10 is written as X. For 030640615 the sum is 130, the remainder is 9, and 11 minus 9 is 2, giving 0-306-40615-2. The tool rejects an X anywhere but the last character.
Converting between the two forms
To go from 10 digits to 13, put 978 in front of the first nine digits and compute a new check digit. To go back, drop the 978 and the old check digit and compute the 10 digit one. A 979 number has no 10 digit form, and the tool says so instead of guessing.
Hyphens and the registration group
Hyphens come from the Agency's October 2026 range table for 26 registration groups, including 978-0, 978-1 and 979-8, which the tool labels "United States." Other groups stay plain digits. Hyphens never affect validity.
Worked examples
- 0-306-40615-2 is valid, with the 13 digit form 978-0-306-40615-7.
- 978-0-306-40615-7 is valid, with the 10 digit form 0306406152.
- 978-0-306-40615-0 is not valid: "Check digit should be 7."
- 080442957X is valid, with the 13 digit form 9780804429573.
- 9798800000009 is valid, shown as 979-8-8000-0000-9 with "None, 979 has no 10 digit form."
- 9780306401657 is valid too. It's 9780306406157 with its 6 and 1 swapped.
The X in the fourth number stands for 10: the weighted sum is 199, the remainder is 1, and 11 minus 1 is 10.
The fifth is a U.S. number from the 979-8 range. The Agency's notice on U.S. prefixes says the U.S. agency now issues 978-0, 978-1 and 979-8 numbers, and that a 979 number has no 10 digit equivalent and must always be recorded in full.
The last is the surprise. The 13 digit check misses an adjacent swap when the two digits differ by 5. Of the 990 ways to swap two different neighboring digits among the first twelve, 110 pass, about 1 in 9. No single wrong digit gets through, and the 10 digit check catches every adjacent swap. A pass is not proof, so compare the digits with the book.
The 13 digit check misses an adjacent swap when the two digits differ by 5.
What a valid result does and does not tell you
Valid means the number is well formed. It doesn't mean the number has been assigned, that it's yours, or that it's the right edition.
To confirm ownership, check the account where you bought the number (in the U.S., ISBNs are sold by Bowker, the U.S. agency). To find its publisher, try the Global Register of Publishers or a library or bookseller catalogue. This tool has no database, so it can't tell you the title.
An ISBN is an identifier, not a copyright. The Agency says it "does not convey any form of legal or copyright protection." Our guide on how to copyright a book explains the difference.
The Agency says it "does not convey any form of legal or copyright protection." Our guide on how to copyright a book explains the difference.
Common mistakes with ISBNs
One number for every format
Paperback, hardcover, ebook and audiobook each need their own.
Trusting a pass
A valid check digit can hide a swapped pair of digits.
An X on a 13 digit number
A 13 digit ISBN never uses X.
Converting a 979 number by hand
It has no 10 digit equivalent.
Tips by situation
Self-publishing
Buy numbers in your own name and check them before uploads. A free platform number names the platform as publisher and can't be moved. See how to get an ISBN.
With a traditional publisher or small press
The publisher assigns the ISBN, so you don't buy one. Use the checker to confirm what a contract or listing shows.
Running a backlist
Paste every ISBN, one a line, and fix each "check it" line before you update retailer metadata.
Related guides on the Author Resources hub
How to Get an ISBN for Your Book
Cost, steps and free versus paid. Read the guide.
How to Copyright a Book
Why an ISBN is not a copyright. Read the guide.
How Much Does It Cost to Publish a Book in 2026?
What a book costs. Read the guide.
When the numbers have to be right on a cover
When we publish a book, the ISBN and barcode are bought at cost in the author's name: $125, or $295 for ten. Print setup is $280 plus printer cost, with files prepared, the spine measured to the paper, and one proof ordered and checked. Every figure is on our published prices page, and our book publishing services show the rest.
When we publish a book, the ISBN and barcode are bought at cost in the author's name: $125, or $295 for ten.
Questions we get asked
How do I check whether an ISBN is valid?
Enter it in the ISBN checker. It weights each digit, adds them up and tests the last digit against the result. A pass means the number is well formed, and a fail shows the check digit it expected. It doesn't confirm who owns the number.
What is an ISBN?
An International Standard Book Number: a 13 digit identifier (10 digits before 2007) for one edition and format of a book, made of prefix, registration group, registrant, publication and check digit. It isn't a barcode or a copyright.
How is the ISBN-13 check digit calculated?
Weight the first twelve digits 1, 3, 1, 3 and so on, add the products, divide by 10 and subtract the remainder from 10. A remainder of 0 gives 0. For 978030640615 the sum is 93, so the check digit is 7.
How do I convert an ISBN-10 to an ISBN-13?
Put 978 in front of the first nine digits, drop the old check digit and compute a new one with the 1 and 3 weights. So 0-306-40615-2 becomes 978-0-306-40615-7. Going back only works for 978 numbers.
Can I look up who published a book from its ISBN?
Not with this tool, because it has no database. Use the Global Register of Publishers for a publisher, or a library or bookseller catalogue for the book.
Does every format need its own ISBN?
Yes. Paperback, hardcover, ebook and audiobook are separate products. A reprint of the same edition keeps its number, and a substantially new edition takes a new one.
How much does an ISBN cost in the US?
As of October 2026, Bowker lists $125 for one number and $295 for ten, or $29.50 each. Some platforms give a free number, but then they're the publisher of record and the number can't move.
Why does my 979 ISBN have no 10 digit version?
979 numbers aren't backward compatible with 10 digit systems, and the Agency warns that forcing a conversion causes duplicates and wrong orders. U.S. numbers starting 979-8 now sit alongside 978-0 and 978-1, so always record all 13 digits.
Keep going with the next tool
Put numbers on the page with the copyright page generator, reserve the barcode area with the cover template generator, or estimate length with the page count estimator. More are on the author tools page.
Tools will only take you so far
Send what you have. Even a half-written manuscript is enough for a reader to tell you what it needs.