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.
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.