ISBN-10 to ISBN-13 Converter

How it is calculated

First the tool removes spaces and hyphens, upper-cases a trailing x, and checks that the input is nine digits plus a final digit or X. It then verifies the ISBN-10 itself: 10×d1 + 9×d2 + … + 1×d10 (X counts as 10) must be divisible by 11, otherwise no result is shown, so a mistyped ISBN-10 is caught. Next it takes the first nine digits, puts 978 in front and drops the old check digit. Over these 12 digits, weights alternate 1, 3, 1, 3 … from the left: check = (10 − sum mod 10) mod 10. The result is the 13 digits without hyphens; the hyphen placement is not restored. Inputs that are already 13 digits are rejected.

Common mistakes

• Just putting 978 in front of the whole ISBN-10, keeping the old check digit; the final digit has to be recalculated, because ISBN-10 and ISBN-13 use different weights.
• Mistyping one digit; the tool checks the ISBN-10 sum and refuses to convert an invalid number rather than producing a valid-looking but wrong ISBN-13.
• Entering a 13-digit ISBN, which is already in the new format and is rejected.
• Entering the X check digit as a letter that looks similar, or dropping it as if it were punctuation; X stands for the value 10 and must stay.
• Assuming every ISBN-13 starts with 978; the tool converts old numbers to the 978 range only, and newer books may use 979, which has no ISBN-10 form.