Barcode labels from Excel

A scanner measures those widths and compares them against the narrowest element it can find. Anything that changes a bar’s width changes what the symbol says, or makes it unreadable.

That is the problem with a barcode embedded as an image. A raster barcode is fixed at the resolution it was made at, and everything that happens to it afterwards nudges bar edges by fractions of a pixel: scaling it to the label, the printer’s own resampling, anti-aliasing at the edges. On screen it looks identical. Under a scanner it is a symbol whose bars are the wrong width.

Here each bar is its own filled rectangle in the PDF, placed at an exact position and width in inches. There is no resolution to lose. Printed at any DPI, the bar edges land where the geometry says they land, and the PDF is pure black on white whatever theme this page is shown in.

A scanner needs blank space either side of a symbol to find where it starts and stops. Every layout here reserves that space explicitly, as data rather than as a happy accident of layout, and no text, border or fill is drawn inside it.

On Avery 5160, for example, a 2-inch symbol is centered on a label 2-5/8 inches wide, leaving 5/16 inch (0.3125 in) clear on each side. For a ten-character value that is over 22 modules, more than twice the minimum.

The rule works the other way too. A very short value has few modules, so each one is wide and ten of them take more room: a one-character value on 5160 is narrowed to 1.83 inches to keep its quiet zones whole.

The narrowest bar in a barcode is called a module, and every character adds modules. A ten-character value that stays in Code 128’s letter set is 145 modules; spread over the 2-inch symbol on a 5160 label, each module is 13.79 mil (thousandths of an inch). Runs of digits switch to a mode that packs two digits into each character, so X001234567 is only 112 modules and prints at 17.86 mil: fewer, wider bars, which scan more easily.

When a value would make the bars too thin, the symbol is widened first, up to the space the quiet zones allow. Only after that does the module width start to fall. Below 10 mil you get a warning in the tool, both in the readout and when you download; below 7.5 mil nothing is generated, because bars that fine will not scan reliably.

The same ten characters on a 4-inch Avery 5163 shipping label get a 3-inch symbol and 20.69 mil bars. If your codes are long, move to a wider label rather than accept thin bars.

If the bars are below 10 mil, the readout under Column to encode says so before you print. Shorten the value or move to a wider label.

Print at actual size. “Fit to page” shrinks every bar by the same percentage, which narrows the modules and the quiet zones together. The PDF asks your viewer to print at actual size, but not every viewer honors it, so check the print dialog.

If width and scaling are right and scans still fail now and then, the variable left is the printer. The calibration sheet prints the same value at four module widths (11, 13, 15 and 17 mil) and two bar heights on one page, so you can find where your own printer and scanner stop agreeing rather than guessing.

Sheet layouts fill a US Letter or A4 page, and you can start on a part-used sheet by picking the first free label on a drawing of the sheet in step 3. Roll layouts put one label on each PDF page at the exact roll size, which is what Zebra, Rollo and DYMO drivers print from. Thermal labels from Excel covers the printer settings.

There are 62 layouts in all. Only the Avery 5160 layout (shared by 8160 and 5260) has been measured on real label stock so far. For any other, print one page on plain paper and hold it against a sheet, or feed a single roll label, before a long run. Every sheet in the label template index has a blank template PDF for that check.