ISBN Converter
Convert ISBN-10 to ISBN-13 and ISBN-13 to ISBN-10, and check that every number is valid. Paste one ISBN or a whole list: each line shows both forms and the check-digit arithmetic behind them. Runs entirely in your browser — nothing is uploaded. Free, no sign-up.
Hyphens, spaces and an ISBN label are ignored. Results are written without hyphens — placing them needs the ISBN Agency's range tables, which this tool does not apply.
Paste an ISBN-10 or ISBN-13 to convert and check it.
How to Use the ISBN Converter
- 1. Paste ISBNs. One per line, with or without hyphens and spaces. Labels such as
ISBN-10:are ignored, and a lower-case x counts as X. - 2. Read each result. A valid line shows its ISBN-13 and ISBN-10; an invalid one says what is wrong — a wrong length, a stray character, an X out of place, or the check digit the other digits call for.
- 3. Open the working. Show the check-digit working lays out every digit, weight and product, the sum, and the remainder that gives the check digit.
- 4. Copy or download. Copy all the ISBN-13s or all the ISBN-10s at once, or download a CSV with every line's result.
How ISBN Check Digits Work
The last digit of every ISBN is calculated from the others, so a single mistyped digit is always caught. ISBN-10's arithmetic also catches every swap of two neighbouring digits; ISBN-13's catches nearly all of them, missing only a swap of two digits that differ by 5. The two lengths use different arithmetic.
ISBN-13: weights 1 and 3, modulo 10
Multiply the first twelve digits alternately by 1 and 3, add the products, and divide by 10. The check digit is 10 minus the remainder — or 0 when the remainder is 0. For 978-0-306-40615-7:
| Position | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Digit | 9 | 7 | 8 | 0 | 3 | 0 | 6 | 4 | 0 | 6 | 1 | 5 |
| Weight | 1 | 3 | 1 | 3 | 1 | 3 | 1 | 3 | 1 | 3 | 1 | 3 |
| Product | 9 | 21 | 8 | 0 | 3 | 0 | 6 | 12 | 0 | 18 | 1 | 15 |
The products add up to 93. 93 mod 10 = 3, and 10 − 3 = 7 — the final digit, so the ISBN is valid.
ISBN-10: weights 10 down to 2, modulo 11
Multiply the first nine digits by 10, 9, 8 … 2, add the products, and divide by 11. The check digit is 11 minus the remainder; a result of 10 is written X and a result of 11 is written 0. For 0-8044-2957-X the products are 0, 72, 0, 28, 24, 10, 36, 15 and 14, which add up to 199. 199 mod 11 = 1, and 11 − 1 = 10 — so the check character is X.
Converting Between the Two
- ISBN-10 to ISBN-13. Put 978 in front of the first nine digits and calculate a new ISBN-13 check digit; the old one is discarded. 0-306-40615-2 becomes 978-0-306-40615-7.
- ISBN-13 to ISBN-10. Only for ISBNs that begin with 978: drop the 978 and the last digit, then calculate an ISBN-10 check digit. 978-0-8044-2957-3 becomes 0-8044-2957-X.
- 979 ISBNs have no ISBN-10. The 979 prefix exists only in the thirteen-digit system introduced in 2007, so no ten-digit ISBN was ever issued for it.
Why the results have no hyphens
Hyphens divide an ISBN into its prefix, registration group, publisher and title number, and the split points depend on ranges the International ISBN Agency publishes and revises. This converter does not apply those tables, so it writes ISBNs without hyphens — a form every catalogue and form accepts. For the hyphenated form, copy it from the book's copyright page.
Frequently Asked Questions
- How do I convert an ISBN-10 to an ISBN-13?
- Prefix the first nine digits with 978 and recalculate the check digit with alternating weights of 1 and 3. Paste the ISBN-10 above to do it instantly: 0-306-40615-2 becomes 9780306406157.
- Can every ISBN-13 be converted to an ISBN-10?
- No. Only ISBN-13s that begin with 978 have an ISBN-10 equivalent. ISBNs that begin with 979 exist only in the thirteen-digit system and have no ten-digit form.
- Why is my ISBN invalid?
- Usually a mistyped or swapped digit, which leaves the check digit out of step with the rest; the converter shows the check digit the other digits call for. Other causes are a missing digit, a letter O typed for a zero, or an X anywhere but the end of an ISBN-10.
- What does the X in an ISBN mean?
- X is the Roman numeral for 10. An ISBN-10 check digit is calculated modulo 11, so it can come out as 10, which is written X to keep the number ten characters long. It appears only as the last character, and never in an ISBN-13.
- Are an ISBN-10 and its ISBN-13 the same book?
- Yes. Converting does not create a new ISBN — it writes the same identifier in the other format. It is different editions and formats, such as hardback, paperback and e-book, that receive different ISBNs.
- Does the converter look the book up?
- No. It only does the arithmetic, entirely in your browser. A valid check digit means the number is well formed, not that it was ever assigned — to find the book itself, use the ISBN Citation Generator or the ISBN to BibTeX Converter.