UPC-A Generator

Enter all 12. We recalculate the check digit and refuse the code if the last digit disagrees, rather than quietly changing it — a barcode with a silently corrected number is worse than an error message, because it scans.

Take the eleven digits, multiply alternate positions by 3 and 1 starting from the right, add them up, and the check digit is whatever brings the total to the next multiple of ten. That is why a single mistyped digit almost always fails the scan instead of pointing at a different product.

The bars are. A UPC-A is an EAN-13 whose leading digit is zero, and modern scanners read both. The difference is administrative: which numbering scheme your products are registered under.

From GS1 in your country, as a company prefix that you then allocate products from. Resellers of individual numbers exist and are cheaper; some marketplaces reject numbers that do not trace back to the seller in the GS1 registry, so check the marketplace’s rules before buying.

The nominal is 37.29 mm wide and 25.93 mm tall including the digits. Retail practice allows 80% to 200% of that. Below 80% the narrow bars approach the resolution of an ordinary scanner and read rates fall off a cliff.

Bars must be dark and the background light, with strong contrast — dark blue or black bars on white or a pale colour. Red bars are the classic mistake: many scanners use red light and see red bars as background.

A little, but the long guard bars at the ends and in the middle must stay long: the scanner uses them to find the edges of the symbol. Truncating the whole code is a known cause of intermittent read failures that only show up at a busy till.