The Five Parts of an ISBN-13
1. EAN Prefix (3 digits)
Every ISBN-13 begins with 978 or 979. These are the EAN (European Article Number) prefixes reserved for books. The 978 prefix is fully allocated; 979 was introduced to expand capacity. Books with 979- ISBNs have no ISBN-10 equivalent.
2. Registration Group (1–5 digits)
The registration group identifies the country or language area responsible for assigning ISBNs in this range. The digit(s) immediately after the EAN prefix are the group number:
- 0 — English-language countries (US, UK, Australia, Canada…)
- 1 — Also English-language (additional capacity)
- 2 — French-language
- 3 — German-language
- 4 — Japan
- 5 — Russian-language
- 7 — China
- 80–94 — Various European and other countries
- 600–649 — Middle East and Central Asia
- 950–989 — Latin America, Africa, and other regions
Each group is managed by a national ISBN agency. See the registration groups directory for all ~160 groups.
3. Registrant / Publisher Prefix (variable length)
After the group number comes the registrant element — the publisher's unique prefix. Larger publishers (with more titles) receive shorter prefixes; smaller presses receive longer ones. A publisher prefix of "596" means O'Reilly Media in group 0. A self-publisher might receive a prefix like "9752298" — seven digits, leaving room for only about 10 publication numbers.
The length of the publisher prefix varies and is determined by the national agency. Use the publisher directory to look up specific prefixes.
4. Publication Number (variable length)
The publication number uniquely identifies the specific title and edition within the publisher's prefix. All nine digits after the EAN prefix must be divided between the group number, publisher prefix, and publication number. The total is always exactly 9 digits (for a 13-digit ISBN).
The more digits used by the group and publisher, the fewer remain for the publication number. A publisher with a 1-digit prefix and a 3-digit registrant has 5 digits for publication numbers — 100,000 possible titles.
5. Check Digit (1 digit)
The final digit is computed from the previous 12 digits using the EAN-13 MOD-10 algorithm. It catches most transcription errors. See the check digit guide for the full calculation.
Reading an ISBN-10
ISBN-10 has the same structure but without the EAN prefix and with only 9 digits for the body:
- Registration group (1–5 digits)
- Registrant/publisher (variable)
- Publication number (variable)
- Check digit (MOD-11, may be X)
Why are hyphens positioned differently in different ISBNs?
Hyphens in an ISBN are not padding — they mark the boundaries between the registration group, registrant, and publication number. Because these segments are variable in length, hyphen positions differ from ISBN to ISBN. Some databases store ISBNs without hyphens to avoid confusion.
When entering an ISBN into a database or book order form, always use the unhyphenated form or follow the system's specific instructions.
Decoding an ISBN by hand
To decode an ISBN without this tool:
- If it's 13 digits, strip the first 3 (EAN prefix: 978 or 979)
- Look up the registration group by matching the first digits to the group table
- Look up the publisher prefix in your national agency's database
- Verify the check digit using the appropriate algorithm
Or just paste it into the decoder tool above — it handles all of this automatically.