Thermal printer settings that stop labels printing wrong

Most label printing problems reported as hardware faults are settings. The printer is fine; it is being handed a page it was never designed to print. Working through these in order fixes the large majority of cases.

Set the page size to the label, not to A4

A 4x6 inch label printer wants a 4x6 inch page. If the document is A4 and the driver is set to A4, the printer will do something reasonable-looking and wrong. Set the stock size in the driver to match the physical label roll, then send a document that is already that size.

Turn scaling off

Options named "Fit to page", "Shrink oversized pages" or "Scale to fit" are the usual cause of barcodes that scan intermittently. Scaling resamples the bars, and a barcode that has been squeezed by 87% has bar widths that no longer match the specification. Set scaling to none, or 100%.

Print from a PDF viewer, not a browser preview

Browser print previews apply their own margins and scaling, and they vary between browsers and versions. Download the PDF and print it from a dedicated viewer, where the scaling control is explicit and stays where you put it.

Check darkness before you blame resolution

Thermal output that looks faint or smudged is usually darkness or speed, not dots per inch. Raising darkness slightly and lowering speed produces crisper edges on the bars. Going too dark bleeds the bars into each other, which fails scanning just as reliably as too light, so adjust in small steps and test with a scanner.

A quick diagnostic

• Label prints but is cut off: page size mismatch.
• Label prints small and centred with white margins: scaling is on.
• Barcode looks fine but scans one time in five: rasterised barcode, or darkness too high.
• Every other label is blank: the document page size is roughly double the label, so one label per two pages.