ISBN-10 vs ISBN-13
An International Standard Book Number identifies one specific edition and format of a book. Until 2007 ISBNs were ten digits long. Since 1 January 2007 every ISBN has been issued as thirteen digits, matching the EAN barcode system used in retail. Older ISBN-10s still appear on backlist books and in some databases, which is why converting between the two is still useful.
An ISBN-13 starts with a prefix — 978 or 979 — followed by groups for the language area or country, the publisher and the title, and ends with a single check digit. ISBN-10s are the same number without the 978 prefix and with a differently calculated check digit.
How the check digit works
ISBN-13
Multiply the first twelve digits alternately by 1 and 3, add up the results, and take the remainder after dividing by 10. The check digit is 10 minus that remainder (or 0 if the remainder is 0). For 978-0-306-40615-?: 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.
ISBN-10
Multiply the first nine digits by 10, 9, 8 … down to 2, add them up, and find the remainder after dividing by 11. The check digit is 11 minus that remainder, taken mod 11 again; a result of 10 is written as X. For 0-306-40615-?: the weighted sum is 130, 130 mod 11 = 9, and 11 − 9 = 2.
Both schemes catch any single mistyped digit, and the ISBN-10 scheme also catches any two swapped neighbouring digits — the two most common copying errors. Open "Show the check-digit maths" under the converter to see the calculation for your own number.
When you'll need this
- Filling in a distributor form that still asks for an ISBN-10, or a library catalogue that lists only one.
- Checking a number before it goes on a cover. A typo in the barcode ISBN is an expensive reprint.
- Cleaning metadata in a spreadsheet of old titles where both forms are mixed together.
Common mistakes
- Re-using one ISBN for several formats. The paperback, hardcover, audiobook and EPUB each need their own ISBN.
- Assuming a 979 number has an ISBN-10. It doesn't, and no converter can make one.
- Treating a valid check digit as proof of registration. It only proves the number is well formed.
- Typing the letter O for zero or l for 1 — the validator will flag it.
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