About this tool
This tool converts ISBN-10 to ISBN-13, converts ISBN-13 back to ISBN-10 where that is possible, and checks whether an ISBN is valid. Paste a single number or a whole list, one per line. Hyphens and spaces are stripped for you, and a lowercase x at the end of an ISBN-10 is accepted.
Each line gets a row showing whether it is valid, the ISBN-13, the ISBN-10 if one exists, and a short note. If a number is wrong, the note says why: the wrong length, characters that cannot be part of an ISBN, or a check digit that should be a different value. If a line is missing its check digit (nine digits for an ISBN-10, twelve for an ISBN-13), the tool works it out and labels it clearly.
It is free, needs no signup, and runs entirely in your browser. Nothing you paste is sent anywhere. It is one of the book tools in our free tools collection.
How it works
An ISBN is a book's International Standard Book Number. Its last digit is a check digit, calculated from the digits before it, so that a mistyped number can usually be caught.
For an ISBN-10, multiply the first nine digits by the weights 10, 9, 8 down to 2, add the products, and take the remainder after dividing by 11. The check digit is 11 minus that remainder, with a result of 11 counting as 0 and a result of 10 written as X. For 0-306-40615-2 the products are 0, 27, 0, 42, 24, 0, 24, 3 and 10, which add up to 130. 130 mod 11 is 9, and 11 minus 9 is 2, which is the check digit.
For an ISBN-13, multiply the first twelve digits alternately by 1 and 3, add them up, and take the remainder after dividing by 10. The check digit is 10 minus that remainder, with a result of 10 counting as 0.
To convert 10 to 13, put 978 in front of the first nine digits, drop the old check digit, and calculate a new ISBN-13 check digit. To go back from 13 to 10, the number must start with 978: drop the 978 and the check digit, then calculate an ISBN-10 check digit. Paste a single ISBN and the tool shows every step, with the weights, the products, the sum and the modulus.
ISBN-10, ISBN-13 and the 2007 switch
ISBNs began as ten-digit numbers in the 1970s. By the early 2000s the supply of ten-digit numbers was running low, and the book trade wanted its numbers to match the EAN-13 barcodes already used across retail. On 1 January 2007 the standard moved to thirteen digits. Books since then carry an ISBN-13, and older books keep their ISBN-10 as well as having an ISBN-13 that is simply the same number with 978 in front.
That is also why you may see a 979 ISBN. The 978 prefix could only hold so many numbers, so the agency began issuing 979 numbers. They exist only as ISBN-13s. A 979 book has no ISBN-10, and any tool that offers you one is guessing. French publishers use the 979-10 range, for example.
The barcode and where to find the ISBN
The barcode on the back cover of a book is the ISBN-13, printed as an EAN-13 barcode. That is the same barcode retailers scan at the till, and the same one Codexia reads with your phone camera. If you can scan it, you do not need to type the digits at all.
You can also find the ISBN printed on the copyright page, usually just after the title page, and often on the back cover above the barcode. Older books may show only the ISBN-10. Listings on bookshops and libraries usually show both.
Practical tips
- If a number comes back invalid, compare it with the book itself. A single wrong digit or two swapped digits is the usual cause.
- Spreadsheets drop leading zeros and turn a trailing X into trouble. Format the column as text before pasting ISBNs in, or you will be checking the wrong numbers.
- A valid check digit does not prove the book exists. It only proves the number is internally consistent.
- The tool gives digits without hyphens. Hyphen positions need the official table of registration group ranges, which changes over time, so we leave them out rather than guess.
Frequently asked questions
How do I convert an ISBN-10 to an ISBN-13?
Put 978 in front of the first nine digits of the ISBN-10, drop the old check digit, then work out a new ISBN-13 check digit. Paste the ISBN-10 above and the tool does all of this for you.
Can every ISBN-13 be converted to an ISBN-10?
No. Only ISBN-13s that start with 978 have an ISBN-10 equivalent. Those starting with 979 were created after the 978 range began to fill up, and they have no ISBN-10 form. The tool says so in the row instead of making one up.
What does the X at the end of an ISBN-10 mean?
X stands for the number 10 in the check digit position, because the check digit is a single character. It can only appear as the last character. You can type it as a capital or lowercase x.
Why does the tool not add hyphens?
The hyphens split an ISBN into registration group, publisher and title, and where the splits fall depends on a table of ranges that the International ISBN Agency updates over time. Guessing without that data gives wrong results, so the tool outputs plain digits.
Can I check a whole list of ISBNs at once?
Yes. Paste one ISBN per line, up to 1,000 lines. Each line gets its own row, and you can copy every ISBN-13 or download the results as a CSV file.
Does this tool check that the book exists?
No. It checks that the number is built correctly, which catches typos and transposed digits. It does not look the number up anywhere, because nothing leaves your browser. A valid ISBN can still be unassigned.