Check Digit Calculator

A check digit is a calculated digit appended to a barcode to verify its accuracy during scanning. It is derived from the other digits using a specific algorithm.

The algorithm multiplies each digit by alternating weights of 1 and 3, sums the products, and calculates the number that rounds the total up to the nearest multiple of 10.

ISBN-10 uses a modulo-11 algorithm with weights decreasing from 10 to 1. The check digit can be 0-9 or X (representing 10).

Check digits catch single-digit errors and most transposition errors. No error-detection scheme catches all errors, but check digits reduce scanning errors significantly.