Barcode check digit calculator

How the check digit works

Every EAN and UPC ends in a digit worked out from the others.

1. Take the digits from the right, not counting the check digit.
2. Multiply the first, third, fifth and so on by three. Multiply the rest by one.
3. Add it all up.
4. The check digit is whatever takes that total up to the next multiple of ten.

The weighting runs from the right. Getting that direction backwards gives you a number that looks right and fails at the till, which is why it is worth checking rather than working out by hand.

A worked example

Take the payload 03600029145, which is eleven digits and so a UPC-A waiting for its last one.

From the right: 5 times three is 15, 4 times one is 4, 1 times three is 3, 9 times one is 9, and so on down the number. The total comes to 58.

The next multiple of ten is 60, so the check digit is 2. The full barcode is 036000291452.

Which lengths mean what

Digits typed	What it is treated as
7	EAN-8 payload, completed
8	Whole EAN-8, checked
11	UPC-A payload, completed
12	Whole UPC-A, checked
13	Whole EAN-13, checked
14	Whole GTIN-14, checked

Twelve and thirteen digits are each two things at once. A twelve digit number is a finished UPC-A and also an EAN-13 missing its check digit. The tool reads both as finished, because checking what you typed cannot invent a digit for a barcode that was already complete.

Why this matters at goods in

A barcode that does not scan gets typed instead, and a typed barcode is where counting errors come from. Getting the number right in the barcode field before the first delivery is far cheaper than fixing it afterwards.

If you are setting up scanning for the first time, the goods in checklist covers the order to do things in. The article on barcode types explains which barcode belongs on which product.