Free ISBN Tool
ISBN Checker, Converter & Book Link Generator
Paste any ISBN — 10 or 13 digits, hyphens optional. We check it's valid, convert between ISBN-10 and ISBN-13 (and the Amazon ASIN), and build a clean canonical Amazon link for every major book marketplace.
How to check if an ISBN is valid
The last character of every ISBN is a check digit — a value calculated from the other digits so that typos are caught automatically. For an ISBN-13, each of the first 12 digits is multiplied alternately by 1 and 3, the results are summed, and the check digit is whatever makes that total a multiple of 10. For an ISBN-10, the digits are weighted 10 down to 2 and the check digit (0–9, or X for 10) makes the weighted sum a multiple of 11. Paste an ISBN above and this tool recomputes the check digit for you — if it matches, you'll see a “Valid ISBN” confirmation.
ISBN-13 check digit: a worked example
Take 978-1-4028-9462-6. The check digit is the final 6. To verify it, multiply the first twelve digits by alternating weights of 1 and 3 and add them up:
9×1 + 7×3 + 8×1 + 1×3 + 4×1 + 0×3 + 2×1 + 8×3 + 9×1 + 4×3 + 6×1 + 2×3 = 104104 mod 10 = 4 → check digit = (10 − 4) mod 10 = 6 ✓The computed check digit is 6, which matches — so 978-1-4028-9462-6 is a valid ISBN. An ISBN-10 works the same way but with weights 10 down to 2 and modulo 11 (where a remainder of 10 is written as X). Paste any ISBN into the checker above and tick “Show the check-digit calculation” to see this breakdown for your own number — valid or not.
Convert an ISBN-13 to ISBN-10 (and to an Amazon ASIN)
For any ISBN-13 beginning with 978, drop the prefix, keep the next nine digits, and recompute the ISBN-10 check digit. That ISBN-10 is also the book's Amazon ASIN, so amazon.com/dp/<isbn-10> is a working product link. The tool shows the ISBN-13, the ISBN-10, and the ready-to-use Amazon links together, and lets you copy any of them.
What is an ISBN?
An ISBN (International Standard Book Number) uniquely identifies a book edition. Every print run, format, and translation gets its own ISBN. Modern books use the 13-digit format (introduced in 2007); older titles use the 10-digit format. The two are mathematically related for any ISBN-13 starting with 978 — and Amazon happens to use exactly that 10-digit form as the ASIN for every book in its catalogue.
Why this matters for authors and book bloggers
If you publish a book on Amazon KDP or review books on your blog, the same title is listed across amazon.com, amazon.co.uk, amazon.de, and the rest of the regional stores — each with its own price, shipping, and (for affiliates) commission tag. Sending every reader to the US store wastes most of your international audience. The right pattern is one canonical link per store, then one geo-routed link wrapping them all.
Common ISBN formats this tool accepts
978-0-306-40615-7(hyphenated ISBN-13)9780306406157(raw ISBN-13)0-306-40615-2(hyphenated ISBN-10)043942089X(ISBN-10 with X check digit)
A note on 979-prefixed ISBNs
ISBN-13s starting with 979 have no 10-digit equivalent — the format simply doesn't exist for them. Amazon listings for these books still use a 10-character ASIN, but it isn't derivable from the ISBN. For 979 titles, search the book on Amazon and use our ASIN Extractor on the resulting URL.
ISBN & book-link FAQ
How do I check if an ISBN is valid?
An ISBN's final character is a check digit computed from the others. For an ISBN-13 you multiply each of the first 12 digits alternately by 1 and 3, sum them, and the check digit is whatever makes the total a multiple of 10. For an ISBN-10 you multiply the digits by 10 down to 2, and the check digit (0–9 or X for 10) makes the weighted sum a multiple of 11. Paste any ISBN above and this tool recomputes that check digit and tells you instantly whether it's valid.
How is the ISBN-13 check digit calculated?
Multiply the first 12 digits of the ISBN-13 by alternating weights of 1 and 3 (first digit ×1, second ×3, third ×1, and so on), then add the products. Take that sum modulo 10; the check digit is (10 − that remainder) mod 10. For example, 978-1-4028-9462-6: 9×1 + 7×3 + 8×1 + 1×3 + 4×1 + 0×3 + 2×1 + 8×3 + 9×1 + 4×3 + 6×1 + 2×3 = 104; 104 mod 10 = 4; check digit = (10 − 4) mod 10 = 6, which matches, so the ISBN is valid. An ISBN-10 uses weights 10 down to 2 and modulo 11 instead (a remainder of 10 is written as X).
How do I convert an ISBN-13 to an ISBN-10 (or an Amazon ASIN)?
For any ISBN-13 that starts with 978, drop the 978 prefix, take the next 9 digits, and recompute the ISBN-10 check digit. The result is the ISBN-10 — which for books is identical to the Amazon ASIN, so amazon.com/dp/<isbn-10> is a valid product link. ISBN-13s starting with 979 have no ISBN-10 equivalent. Paste an ISBN above and the tool shows both formats and the ASIN.
What is the difference between ISBN-10 and ISBN-13?
Every book published since 2007 has a 13-digit ISBN. Books published before that have a 10-digit ISBN. The two are mathematically related when the ISBN-13 starts with 978 — you can convert between them by recomputing the check digit. ISBN-13s starting with 979 have no ISBN-10 equivalent.
Why does Amazon use ISBN-10 instead of ISBN-13 in URLs?
Amazon uses a 10-character ASIN (Amazon Standard Identification Number) to identify every product. For books, the ASIN is identical to the ISBN-10. That is why amazon.com/dp/0306406152 works as a canonical book link.
Will the same ISBN work on amazon.co.uk, amazon.de, and amazon.co.jp?
Usually yes for English-language and widely distributed titles, but Amazon maintains separate catalogues per region. A US edition may not be listed on amazon.co.jp, and translated editions have their own ISBNs. Always click through to confirm before sharing internationally.
How do I send international readers to the right Amazon store automatically?
Wrap any of the generated per-country URLs in a single geo-smart-link. Visitors from the UK get routed to amazon.co.uk, visitors from Germany to amazon.de, and so on — from one short link in your bio, podcast notes, or email signature.