Question 1

Does this tool look up book details from the ISBN?

Accepted Answer

No. This tool only checks structural validity — whether the ISBN's check digit matches the required checksum (mod-11 for ISBN-10, mod-10 for ISBN-13) — and converts between the ISBN-10 and ISBN-13 formats. It does not look up titles, authors, or covers from any book database. Nothing you enter is ever sent anywhere; every check runs in your browser.

Question 2

How is an ISBN-10 checksum calculated?

Accepted Answer

Each of the first 9 digits is multiplied by a weight counting down from 10 to 2, and the products are summed. The check digit (the 10th character) is whatever value makes that sum, including the check digit itself, divisible by 11. If the required check value is 10, it is written as the letter X instead of a two-digit number.

Question 3

How is an ISBN-13 checksum calculated?

Accepted Answer

ISBN-13 uses the same EAN-13 barcode checksum as any retail barcode: each of the first 12 digits is multiplied alternately by 1 and 3, the products are summed, and the check digit is whatever value makes that sum divisible by 10.

Question 4

Can every ISBN-13 be converted to an ISBN-10?

Accepted Answer

No. Only ISBN-13s starting with the "978" prefix can be converted to ISBN-10, because ISBN-10 was retired before the "979" prefix range was introduced. A 979-prefixed ISBN-13 (increasingly common for newer books) has no ISBN-10 equivalent at all.

Question 5

Why does my ISBN show as invalid even though it looks right?

Accepted Answer

An ISBN can fail for two independent reasons: the check digit may not match the checksum formula (often a typo), or — for ISBN-13 — the number may not start with the '978' or '979' Bookland prefix reserved for books, even if its checksum happens to be mathematically valid.

Question 6

Does this tool support hyphens in ISBNs?

Accepted Answer

Yes. Hyphens and spaces are automatically stripped before validation, so you can paste an ISBN exactly as printed on a book (e.g. "978-0-306-40615-7") or as a plain 10 or 13 character string.

ISBN Validator & Format Converter

Enter an ISBN

Results

Frequently Asked Questions

Does this tool look up book details from the ISBN?

How is an ISBN-10 checksum calculated?

How is an ISBN-13 checksum calculated?

Can every ISBN-13 be converted to an ISBN-10?

Why does my ISBN show as invalid even though it looks right?

Does this tool support hyphens in ISBNs?

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