ISBN validator and converter

Two kinds of ISBN

Every edition of a book gets an International Standard Book Number. Until 2007 ISBNs had 10 digits; since then they have 13, matching the EAN-13 barcode on the back cover. An ISBN-13 starting with 978 has an equivalent ISBN-10, which is why older catalogues and Amazon's ASINs for books still use the 10-digit form.

Both end with a check digit. ISBN-10 uses a modulo 11 check, so its last character can be X (meaning 10). ISBN-13 uses the barcode check with weights 1 and 3. Either catches every single-digit typo.

Worked example

ISBN-10 0-306-40615-2: 0×10 + 3×9 + 0×8 + 6×7 + 4×6 + 0×5 + 6×4 + 1×3 + 5×2 = 130, and 130 mod 11 = 9, so the check digit is 11 − 9 = 2. The ISBN-13 is 978 + 030640615 + a new check digit: 9780306406157.

The page removes hyphens and spaces, recognises ISBN-10 (9 digits plus a digit or X) or ISBN-13 (13 digits starting 978 or 979), and checks the final digit. For ISBN-10 the first nine digits are weighted 10 down to 2 and the check digit makes the total divisible by 11. For ISBN-13 the digits are weighted 1 and 3 alternately, as in EAN-13 barcodes, and the check digit makes the total divisible by 10. It then converts: ISBN-10 to ISBN-13 by adding 978 and a new check digit, and ISBN-13 with prefix 978 back to ISBN-10. Everything runs in your browser.