Should you print darker or lighter?
Lighter, if a barcode is failing. Our testing found that barcodes stop scanning because the white gaps between bars close up, not because the black bars fade. A darker or “best quality” print setting lays down more toner or ink, and that spreads and closes those gaps faster. If a small barcode won’t scan, the fix is a bigger print or a lighter setting, not a darker one.
What’s the single easiest thing to get wrong?
Trusting your print dialog’s idea of “100%.” Many desktop and mobile print dialogs silently scale pages down a few percent to fit the printer’s non-printable margin, with no visible warning. On the printer we tested, a line specified at 100 mm printed at 96 mm: a 4% shrink that’s easy to miss and large enough to push a barcode already near its size limit past the point of scanning reliably.
Before trusting any printed barcode dimension, print a line of known length, measure it with a ruler, and adjust from there. On desktop, choose “Actual size” or “100%” rather than “Fit to page.”
Does paper choice matter?
Less than print settings, but it’s not nothing. A rougher or more absorbent paper lets ink or toner spread further than a smooth label stock, which has the same effect as printing too dark: the gaps between bars close faster. If a barcode is marginal on plain paper, switching to a smoother label stock can help even at the same print settings.
What size should you print at?
Whatever GS1’s magnification range allows for retail, or whatever scans reliably on your own equipment for internal use. Our measured minimums (the smallest size each format still scanned at in testing) are on the barcode generator page, alongside the full test setup and method, so you can reproduce it with your own printer and see whether the numbers hold.