A technical deep dive into why your PDF labels might not be printing correctly.
Understanding PDF Page Sizes
A4 (8.27 x 11.69 inches)
This is the standard document size in most of the world. Many carriers generate labels on A4 sheets, often putting 2 or 4 labels on one page.
Letter (8.5 x 11 inches)
Standard in the US. Similar issues to A4 when printing on thermal printers.
4x6 inches
The standard for thermal shipping labels. This is what you want.
The Problem
If you send an A4 PDF to a printer expecting 4x6, it will shrink the whole A4 page to fit 4x6, making the label tiny. You need to crop the A4 page to just the label area before printing.