A barcode that scans, at the size it will be printed BARCODE
Two things go wrong with barcodes made on the web, and both are found after the labels are printed: a check digit that does not agree, and a symbol scaled to fit a box, which loses its module width.
What to encode
How big
The module is the width of the narrowest bar and it is the size that matters. The quiet zone is part of the symbol rather than a margin: without clear space either side, many scanners never find the start.
The barcode
How it works
Barcodes made on the web usually fail after the labels are printed: a check digit that does not agree, or bars too narrow to scan at the printed size. BARCODE makes barcodes, including Code 128, with the check digit worked out, sized to the width they will actually be printed, and exports SVG for sharp printing. It tells you when it has corrected a check digit. Your data stays in this tab.
Doing this often? OBSCURA Vector places the barcode in a finished label or packaging design and exports SVG or PDF for print. On its own, US$4 a month; with everything else, US$9 a month or US$79 a year. 7 days free.