ISBN check digit validator
Validate an ISBN-10 or ISBN-13 check digit, hyphenate common English groups, and convert between 978 forms.
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Tool guide
ISBN check digit validator: how it works
Practical information to understand the result and use this tool correctly.
About ISBN check digit validator
ISBN-13 uses a mod-10 check. For the first 12 digits, weights alternate 1 and 3. The check digit is (10 − (sum mod 10)) mod 10.
ISBN-10 uses a mod-11 check on the first 9 digits, weighted 10 down to 2. A remainder of 10 is written X. Hyphens and spaces do not count.
A 978 ISBN-13 converts to ISBN-10 by dropping 978, keeping the next 9 digits, and recalculating the mod-11 check. 979 forms have no ISBN-10 equivalent.
How to use it
- 1Paste an ISBN-10 or ISBN-13. Hyphens and spaces are optional.
- 2Read whether the check digit matches, and the expected digit if it does not.
- 3Copy the compact form, the converted 978 pair, or the hyphenated English-group form.
- 4Reset or load a preset. Nothing is uploaded.
Frequently asked questions
- Is 978-0-306-40615-7 valid?
- Yes. Compact 9780306406157. The first 12 digits with weights 1,3,1,3… sum to 93. 93 mod 10 is 3, so the check digit is (10−3) mod 10 = 7. The ISBN-10 form is 0306406152.
- How is the ISBN-10 check digit calculated?
- For 030640615 the weighted sum is 0×10+3×9+0×8+6×7+4×6+0×5+6×4+1×3+5×2 = 130. 130 mod 11 is 9, and (11−9) mod 11 is 2. The full ISBN-10 is 0-306-40615-2.
- What if the check digit is wrong?
- 9780306406158 fails: the formula still expects 7. The tool marks it invalid and shows the corrected ISBN-13 9780306406157. It does not treat a wrong digit as valid.
- What about empty, X, or the wrong length?
- An empty field is an error. X is allowed only as the ISBN-10 check digit. 9 or 11 characters, a negative sign, or a 979 number with X are rejected. Zero is not a special ISBN; 0000000000000 fails the 978/979 prefix check.