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
Questions people ask about BARCODE