Every published book in the world is assigned a unique International Standard Book Number (ISBN). The ISBN system includes a built-in check digit — the last digit — computed mathematically to catch transcription errors. There are two formats: the older 10-digit ISBN-10 (used before 2007) and the current 13-digit ISBN-13 (which is also a valid EAN-13 barcode). This checker validates either format, shows the check digit calculation, and converts between formats.
How to Use the ISBN Checker
Enter any ISBN with or without hyphens/spaces. The tool:
- Auto-detects whether it's ISBN-10 or ISBN-13
- Validates the check digit using the correct algorithm
- Shows the math — each digit multiplied by its weight, the sum, and the check digit formula
- Converts between ISBN-10 and ISBN-13 if applicable
ISBN Check Digit Algorithms
ISBN-10: Multiply each of the first 9 digits by weights 10, 9, 8, ..., 2. Sum all products. The check digit makes (sum + check) mod 11 = 0. If the check digit is 10, it's written as 'X'.
ISBN-13: Uses the same GS1 algorithm as EAN barcodes — alternating weights of 1 and 3. The check digit makes (sum + check) mod 10 = 0.
Understanding ISBN Structure
An ISBN-13 like 978-0-545-01022-1 breaks down as:
- 978 — GS1 prefix (978 or 979 for books)
- 0 — Registration group (English-speaking countries)
- 545 — Publisher code (Scholastic)
- 01022 — Title code
- 1 — Check digit
ISBN-10 omits the 978 prefix and uses a different check digit algorithm.
Step-by-Step Instructions
- 1Enter an ISBN (10 or 13 digits, with or without hyphens).
- 2The tool auto-detects the format and validates the check digit.
- 3View the step-by-step calculation showing each digit's weight and product.
- 4If valid, see the converted ISBN in the other format.
- 5Copy the validated ISBN or conversion result.