ISBN Check Digit Calculator.
Enter a 12-digit ISBN prefix to calculate its check digit, or a full 13-digit ISBN to validate it. Useful for self-publishers preparing metadata for KDP, IngramSpark, or print distributors.
Dashes and spaces are ignored. Enter the 12-digit prefix of an ISBN-13 to calculate its check digit, or all 13 digits to verify an existing ISBN is valid.
Processed on our server. What you enter is sent over an encrypted connection, calculated, and returned. It is never written to a database or logged, and nothing is retained once the result is sent. Avoid entering passwords, API keys or other secrets. How we handle data
Why This Matters for Self-Publishers
A mistyped ISBN in your metadata can cause a print listing to fail validation at IngramSpark or KDP, or cause a bookstore's ordering system to pull up the wrong title entirely. Checking the digit before submission catches the error early.
Generate vs Validate
Enter 12 digits to calculate what the 13th (check) digit should be. Enter all 13 digits of an existing ISBN to confirm whether the check digit it already has is correct.
ISBN Check Digit Calculation Methodology.
The Calculation Branch
Industrial Standards.
Each of the first 12 digits is multiplied by 1 if it's in an odd position (1st, 3rd, 5th...) or 3 if it's in an even position (2nd, 4th, 6th...). The twelve products are summed, and the sum is reduced modulo 10. Subtracting that remainder from 10 gives the check digit (using 0 if the remainder is already 0). This weighting scheme is identical to the one used by UPC and EAN-13 retail barcodes, which is why ISBN-13 numbers can be printed directly as scannable barcodes.
In-Depth Analysis & Reference Data
Every published ISBN-13 begins with either 978 or 979 — the EAN 'Bookland' prefix that tells scanning systems the barcode identifies a book rather than a general retail product. After the prefix comes a registration group identifier (which country or language area issued it), a registrant identifier (the publisher), and a publication identifier (the specific title and edition), followed by the check digit calculated here.
If you're preparing print files for IngramSpark or formatting metadata for an aggregator, double-check that the ISBN in your interior file's copyright page matches exactly what you submitted in the metadata form — mismatches between the two are a common cause of print proof delays.
Registry Questions & FAQ.
Does a different ISBN-13 apply to ebook vs paperback editions?
Yes. Each distinct format and edition of a book — hardcover, paperback, and ebook — should have its own unique ISBN, since the ISBN identifies a specific manifestation of a work, not just the title. Amazon KDP ebooks use Amazon's internal ASIN instead of requiring a separate ISBN, but paperback and hardcover editions need one.
I entered 13 digits and it says invalid — what should I check first?
First confirm you copied all 13 digits correctly with no transposed pairs. If it's still invalid, the ISBN may have been entered incorrectly at the source (a publisher database or book listing) — cross-check it against the physical book's back cover or copyright page barcode.
Estimates for planning. Always confirm against an authoritative source.