Barcode Check Digit Calculator
Already have a barcode number and just need to work out or double-check its check digit? Pick a format, enter your digits, and this tool calculates the correct check digit instantly — or tells you whether one you already have is right. No barcode image required, though a live preview and download is included below in case you want one. Ready to make the actual barcode image? Try the UPC & EAN Barcode Generator, ITF-14 Barcode Generator, or Code 39 Barcode Generator.
Barcode Number
How to Use
- Choose the barcode format your number belongs to.
- Type in the digits (or, for Code 39, the data characters). Leave off the check digit to have it calculated, or include it to verify whether it's correct.
- The result updates instantly as you type — no button to click.
- A live barcode preview appears below the result once a valid number is entered, with PNG and SVG download options.
How the Check Digit Is Calculated
UPC-A, EAN-13, EAN-8, and ITF-14 all use the same GS1 weighted check-digit formula, regardless of length: starting from the rightmost data digit, each digit is alternately multiplied by 3 and by 1, the results are summed, and the check digit is whatever value brings that sum up to the next multiple of 10.
Code 39 uses a different method: every character in the data (digits, letters, and the supported symbols) has an assigned numeric value from 0–42, the values are summed, and the sum modulo 43 is looked up back in the same table to find the check character.
Frequently Asked Questions
Why would I need to calculate a check digit manually?
It's useful for validating a list of product numbers before importing them into inventory software, checking a number that was transcribed by hand, or understanding what check digit a system will expect for a number you're about to register.
What if I enter the wrong number of digits?
The help text under the input tells you exactly how many digits (or the two acceptable lengths, with or without a check digit) the selected format expects.
Does this work for Code 39 too?
Yes — Code 39 uses a completely different check-digit algorithm (modulo 43 instead of the weighted modulo 10 used by UPC/EAN/ITF-14), and this tool handles both automatically based on the format you select.
Can I download an actual barcode once I have a valid number?
Yes — once your number (or data) is valid, a barcode preview appears automatically with PNG and SVG download buttons.
Is my data uploaded anywhere?
No. Every calculation happens locally in your browser — nothing you enter is sent to a server.
