About the ISBN Converter
Every book has an ISBN, the International Standard Book Number. Older books carry a 10-digit number and newer ones a 13-digit one that begins with 978 or 979. This tool checks that the check digit is right and converts between the two forms. Type the number with or without hyphens; an ISBN-10 may end in X, which stands for 10. Type an ISBN-10 or ISBN-13 and the ISBN appears at once, with a few related figures underneath, and you can copy the result with one tap. The sums run in your browser, so nothing you enter is uploaded.
Updated October 2026
How to use the ISBN Converter
- 1Enter an ISBN-10 or ISBN-13.
- 2Pick the units or options from the menus if the ISBN tool offers them.
- 3Read the ISBN in the large result box.
- 4Look at the extra rows for related figures.
- 5Press Copy result to keep the answer.
When you need the ISBN
Librarians, booksellers and online shops use both forms, and software often needs one or the other. Readers use the tool to find the same book across catalogues, and to check that an ISBN copied from a page has no typo.
The groups in a hyphenated ISBN show the registration group, the publisher and the title, but their lengths vary, so this tool does not add hyphens. It shows the plain digits.
How the ISBN is worked out
ISBN-10: the digits times 10, 9, 8 … 1 add up to a multiple of 11. ISBN-13: the digits times 1, 3, 1, 3 … add up to a multiple of 10. To convert ISBN-10 to ISBN-13, put 978 in front of the first nine digits and work out a new check digit. The ISBN-10 0-306-40615-2 is valid and becomes the ISBN-13 978-0-306-40615-7. Going back, 978-0-306-40615-7 gives 0306406152. An ISBN-13 starting with 979 has no ISBN-10 form.
Every answer on this page comes from that one rule, so you can check any result by hand with a calculator. The figures shown underneath, such as other units, are conversions of the same answer.
- Both directions
- Check digit test
- Hyphens ignored
Mistakes to avoid with ISBN
A correct check digit does not mean that the book exists or that the number is assigned. It only shows that the digits are consistent. The check digit of an ISBN-10 can be X, but never in an ISBN-13.
On phone and computer
On a phone, type into the boxes one after another and read the ISBN underneath; Copy result puts it on the clipboard for a message or a note. On a computer the inputs sit on the left and the answer on the right, so you can change one figure and watch the ISBN move. The isbn converter works the same on both. Book numbers follow a check rule, so related tools can spot mistakes. Use the Check Digit Calculator to see how the last digit is made, the Barcode Generator to print a code, and the Luhn Validator for card-style numbers that follow another rule.
Features
- 978 numbers convert
- X means 10
- 979 has no ISBN-10
- Clear messages when the ISBN inputs make no sense
- Copy the result with one tap
- Private: nothing is uploaded
Frequently asked questions
How do I calculate ISBN?
ISBN-10: the digits times 10, 9, 8 … 1 add up to a multiple of 11. ISBN-13: the digits times 1, 3, 1, 3 … add up to a multiple of 10. To convert ISBN-10 to ISBN-13, put 978 in front of the first nine digits and work out a new check digit. The ISBN-10 0-306-40615-2 is valid and becomes the ISBN-13 978-0-306-40615-7. Going back, 978-0-306-40615-7 gives 0306406152. An ISBN-13 starting with 979 has no ISBN-10 form.
What is the formula for ISBN?
ISBN-10: the digits times 10, 9, 8 … 1 add up to a multiple of 11. ISBN-13: the digits times 1, 3, 1, 3 … add up to a multiple of 10. To convert ISBN-10 to ISBN-13, put 978 in front of the first nine digits and work out a new check digit. The isbn converter applies it exactly and rounds only the displayed answer to six significant figures.
Why does an ISBN-10 end in X?
The check digit is calculated modulo 11 and the value 10 is written as X.
Can every ISBN-13 become an ISBN-10?
No. Only those that begin with 978 can.
Which ISBN do I use?
ISBN-13 is the current standard since 2007.
Is this isbn converter free and private?
Yes. It is free, needs no account and runs in your browser, so the numbers you type are not uploaded or stored.