How to use it
- Type the number from the back of the book or the barcode in ISBN or barcode number. Hyphens and spaces are fine.
- Read Result: green means the check digit is right; red shows the digit the rule needs.
- Use Converted to get the ISBN-13 of an ISBN-10, or the ISBN-10 of a 978 ISBN-13.
- Read How the check digit was worked out to see the sum and the remainder.
How the check digits work
An ISBN-10 has ten characters. Its digits are weighted 10 down to 2 and added; the total must be a multiple of 11, and a final X stands for 10. An ISBN-13, an EAN-13 and a GTIN-14 use the GS1 rule: from the right, the digit before the check digit has weight 3, the next weight 1, and so on. The check digit makes the total a multiple of 10.
GS1: check = (10 − (weighted sum mod 10)) mod 10, weights 3 and 1 from the right
ISBN-10: the sum of (10 − position + 1) × digit, with X = 10, must be a multiple of 11- An ISBN-13 is an EAN-13 whose prefix is 978 or 979, so both are checked the same way.
- UPC-A (12 digits), EAN-8 (8 digits) and GTIN-14 (14 digits) use the same GS1 rule.
What the GS1 prefix tells you
The first digits of an EAN-13 are a GS1 prefix. The GS1 Company Prefix page lists a range of prefixes for each country or GS1 service: for example 868 and 869 for Türkiye, 400 to 440 for Germany, and 978 and 979 for books (ISBN). This tool shows the label of the range that contains the prefix. A prefix the page does not list shows no country.
- A prefix shows which numbering organisation issued the company number. It does not show where a product was made or sold.
- The check digit proves only that the number is well formed. It does not show that a book or product exists.
Worked example: 0306406152 (ISBN-10)
The first nine digits 0 3 0 6 4 0 6 1 5, weighted 10 down to 2, give 0 + 27 + 0 + 42 + 24 + 0 + 24 + 3 + 10 = 130. The remainder of 130 on division by 11 is 9, so the check character is (11 − 9) mod 11 = 2, which is the last digit typed.
With the check digit included the total is 132 = 12 × 11, a multiple of 11, so the number is valid.
The ISBN-10 converts to 9780306406157 by putting 978 in front and recalculating the check digit.
| Item | Value |
|---|---|
| Type | ISBN-10 |
| Converted | ISBN-13: 9780306406157 |
| Result | Valid |
Frequently asked questions
How do I know which barcode type I have?
The page reads the length: 10 characters is an ISBN-10, 13 digits is an ISBN-13 or EAN-13, 12 digits is UPC-A, 8 digits is EAN-8 and 14 digits is GTIN-14.
Why does an ISBN-10 sometimes end in X?
The check character can be 10, which cannot be one digit, so the ISBN standard writes it as X. The page accepts X only as the last character.
Does a valid check digit mean the book or product is real?
No. The check digit confirms the number is well formed. It does not show that the book exists, is in print, or that the product is genuine.
Why is no country shown for my EAN-13?
The GS1 page lists the prefixes it assigns to countries and to GS1 services. A prefix it does not list has no label, so the page says that no country is listed rather than guess one.
Can I convert an ISBN-13 that starts with 979?
No ISBN-10 exists for a 979 number, because the ISBN-10 form only covers numbers starting with 978. The page says so.
Does the page keep the code I type?
No. The check runs in your browser and nothing is stored or sent.
Sources
- GS1: General Specifications, check digit calculation (section 7.9.1)
- GS1: how to calculate the check digit manually
- GS1: Company Prefix (GS1 prefixes and country list)
- ISBN International: what is an ISBN
Figures and text last checked on Tuesday, November 10, 2026.