Free ISBN Converter
Convert book identifiers between 10-digit and 13-digit formats in real time. Our free converter handles single numbers and batch lists with automatic format detection.
Designed for publishers, authors, and librarians managing legacy book databases and modern catalog uploads.
Convert Your ISBN
Enter an ISBN-10 or ISBN-13 number below. The tool detects format and converts accordingly.
How ISBN Formats Compare
On January 1, 2007, the International ISBN Agency transitioned from 10-digit to 13-digit numbers to expand global numbering capacity and align with the GS1 retail barcode standard.
| Attribute | ISBN-10 (Legacy) | ISBN-13 (Current Standard) |
|---|---|---|
| Standard Length | 10 characters | 13 digits |
| GS1 Bookland Prefix | None | 978 or 979 |
| Check Digit Algorithm | Modulo 11 (weights 10 down to 2) | Modulo 10 (alternating weights 1 and 3) |
| Check Character Set | Digits 0-9 plus Roman numeral X | Digits 0-9 only |
| EAN Barcode Matching | Requires prefix addition | Direct 1:1 match with EAN-13 |
| Active Assignment | Discontinued in 2007 | Active global standard |
Why 979 ISBNs Cannot Convert to ISBN-10
Only ISBN-13 numbers starting with prefix 978 map back to a 10-digit identifier. The 979 prefix represents a completely new pool of numbers introduced after 2007.
Important Rule: If your book was assigned an ISBN starting with 979, do not attempt to convert it to 10 digits. Use the 13-digit number across all publishing platforms.
Frequently Asked Questions
What is the main difference between ISBN-10 and ISBN-13?
ISBN-10 is the legacy format used before 2007. ISBN-13 is the current international standard aligned with EAN-13 barcodes. All new books receive 13-digit identifiers.
Can all ISBN-13 numbers convert to ISBN-10?
No. Only ISBN-13 numbers starting with prefix 978 can convert to ISBN-10. ISBN-13 numbers starting with prefix 979 have no 10-digit equivalent.
Why do ISBN-13 numbers starting with 979 lack an ISBN-10 version?
The international ISBN agency introduced prefix 979 after the 978 pool was exhausted. Prefix 979 was never part of the legacy 10-digit system.
How does the conversion algorithm work?
To convert ISBN-10 to ISBN-13, add the 978 prefix to the first 9 digits and recalculate the Modulo 10 check digit. To convert back, drop 978 and recalculate Modulo 11.
Why does the check digit change during conversion?
ISBN-10 uses Modulo 11 weighting, while ISBN-13 uses Modulo 10 alternating weighting. Changing the formula changes the resulting check digit.
Can I convert multiple ISBNs at once?
Yes. Switch to the Multiple ISBNs tab to convert batches of numbers simultaneously.
Are hyphens preserved during conversion?
The converter outputs clean numerical strings. You can then use our free hyphenator tool to add official group hyphens.
Do modern bookstores still ask for ISBN-10?
Most modern retailers use ISBN-13. However, some legacy library systems and distributor databases still store 10-digit cross-references.
Related Publishing Resources
Check Digit Calculator
Calculate missing checksum digits using Modulo 10 and Modulo 11 formulas.
ISBN Validator
Validate complete ISBNs against checksum rules in single or batch modes.
ISBN Hyphenator
Add standard hyphen placement based on official registration agency data.
Get Official ISBNs
Acquire registered US publisher ISBNs for all print and digital book editions.