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Barcode Check Digit

Calculate or verify the check digit of common barcode and ISBN formats, with the weighting shown.

Check digit calculator

Check digit: —
Full code: —
Weights used: —
Verification: —
Enter the digits without the check character for compute mode, or the whole code for verify mode.

How to use the Barcode Check Digit

  1. Choose the symbology, such as EAN-13, UPC-A or ISBN-10.
  2. Enter the digits without the check character, or the whole code to verify.
  3. Read the check digit, the full code and the weighting table below.

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Frequently Asked Questions

Common questions about the free online barcode check digit.

A check digit is an extra character calculated from the other digits of a code, so that scanning or typing errors can be detected automatically.
The first twelve digits are multiplied by alternating weights of one and three, the products are summed, and the check digit makes that total a.
UPC-A uses eleven body digits and starts the alternating weight pattern with three instead of one, but the modulo ten rule is the same.
The nine characters are multiplied by weights from ten down to two, summed, and the result is completed modulo eleven. A remainder of ten becomes X.
Code 39 has forty three possible characters, so each character has a value and the check character is chosen by reducing their sum modulo forty three.
It lists every character with its value, the weight applied to it and the resulting product, followed by the sum, the modulo step and the final check.
In compute mode enter the code without its check digit. In verify mode enter the whole code and the tool will confirm whether the check character is.
Yes. ITF-14 uses thirteen body digits with alternating weights of three and one, exactly like the other modulo ten formats.
No. Every check digit is computed locally in your browser, so the codes you type are never uploaded or stored.

Last updated: October 10, 2026