Printing barcode labels: sizes, printers and quiet zones

A printed barcode can fail to scan for a few reasons. This page covers the ones the saved sources describe: space around the code, the scanner's dot of light, code length and the check digit.

The quiet zone

A quiet zone is the blank margin on each side of the bars. Scanners use it to find where the code starts and stops.

• UPC-A. A quiet zone of at least 9 times the x-dimension must be present on each side of the scannable area. The x-dimension is the width of the narrowest bar.¹
• Code 128. The minimum quiet zone to the left and right is 10x, where x is the minimum width of a module.²
• On the label. Don't print a border, a logo or a line of text into that margin. Don't let a label's edge cut it off.
• In the design tool. Leave extra blank space on both sides rather than trimming to the bars.

Bars

• Scanner resolution. It is measured by the size of the dot of light the reader emits. If that dot is wider than any bar or space, it overlaps two elements and may give wrong output. A dot that is too small can also misread spots on the code.³ Test a label with your own scanner.

Length and distance

• Long codes read from further back. The longer a Code 128 barcode is, the greater the distance a laser reader needs from it.² Shorter SKUs help here, as the numbering page explains.
• A wider label may be needed. If a longer code doesn't fit, a bigger label beats a tiny code.

Printers and label sizes

• Follow the printer maker's manual. Label widths, print resolution, ribbon or thermal settings and darkness differ between models. Your manual is the place to look.
• Choose a label size from your code. The label has to hold the bars plus the quiet zones at both ends, with room for the human-readable number.
• Buy one roll and test it first. Then order more of the same stock.
• Retail symbols follow set rules. If you plan to sell through shops, ask your national barcode office what it expects. The numbers inside UPC and EAN symbols are assigned through GS1.¹ Sourcing product numbers has more.

Check the number too

• Check digit. It's an extra digit used to verify that a barcode has been scanned correctly.⁴- Right type for the data. A code with letters can't go in a numbers-only type. See common barcode types.
• Matches the record. The printed code must be exactly what your software holds. A mismatch can mean a scan finds no item; this page on software shows one example.

Testing

• Try a different scanner. Omnidirectional scanners are better at reading poorly printed, wrinkled or torn barcodes, so a different scanner may read a poorly printed code better.³
• Use a verifier for big runs. A barcode verifier works the way a reader does, but it runs a series of tests, including proper spacing of elements.⁵ Check whether your national GS1 office offers verification.

If a code still won't scan, try a different scanner type before you reprint the lot.