ISBN-10 to ISBN-13 Converter and Checker
Paste any ISBN to check that it's valid and get both the 10-digit and 13-digit versions.
How ISBN check digits work
The last digit of every ISBN is a check digit calculated from the others, so a typo in any single digit is caught.
ISBN-13
sum = d1×1 + d2×3 + d3×1 + d4×3 + … + d12×3
check = (10 − sum mod 10) mod 10ISBN-10
sum = d1×10 + d2×9 + … + d9×2
check = (11 − sum mod 11) mod 11, with 10 written as XConverting ISBN-10 to ISBN-13
Drop the old check digit, put 978 in front, and calculate a new ISBN-13 check digit. Going the other way, remove the 978 prefix and the last digit, then calculate an ISBN-10 check digit.
Worked example
ISBN-10 0-306-40615-2: drop the final 2, add 978 to get 978030640615, and calculate the check digit. The weighted sum is 9×1 + 7×3 + 8×1 + 0×3 + 3×1 + 0×3 + 6×1 + 4×3 + 0×1 + 6×3 + 1×1 + 5×3 = 93. 93 mod 10 = 3, and 10 − 3 = 7, so the ISBN-13 is 9780306406157.
Where the ISBN goes on your book
The ISBN-13 goes on the copyright page of the interior and in the barcode on the back cover. If you use KDP's free ISBN, KDP adds the barcode for you; leave the barcode area on your cover clear. Each format needs its own ISBN: paperback and hardcover editions get different numbers, and a new edition with substantial changes needs a new ISBN too.
Frequently asked questions
Can every ISBN-13 be converted to ISBN-10?
No. Only ISBN-13s that start with 978 have an ISBN-10 equivalent. Numbers starting with 979 were issued after the switch to 13 digits and exist only as ISBN-13.
Why does an ISBN-10 sometimes end in X?
The ISBN-10 check digit is calculated modulo 11, so it can be 10. A single "X" (the Roman numeral for 10) is used so the number stays 10 characters long.
Do I need my own ISBN for KDP?
No. KDP offers a free ISBN for paperbacks and hardcovers, but KDP is then listed as the imprint and you can only use that ISBN on KDP. Buying your own (from Bowker in the US, Nielsen in the UK, or your national agency) lets you use it with any printer.
Does a Kindle ebook need an ISBN?
No. Amazon assigns its own ASIN to Kindle ebooks. An ISBN is optional.
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