203 vs 300 vs 600 DPI

DPI is the number of printable dots per inch. Higher DPI creates more addressable dots over the same physical distance, so a ZPL coordinate cannot be transferred blindly between resolutions.

Physical size stays the same

A 100 mm label is still 100 mm wide at every resolution. What changes is the integer dot count used by the printhead. That is why the same ZPL dimensions can print at the wrong physical size after moving a format between printers with different DPI.

Choosing a resolution

Resolution choice depends on printer hardware and the detail your application requires. Small text, fine graphics and compact barcodes can benefit from higher resolution, while many general shipping and warehouse labels are designed around lower-resolution printheads. Follow the printer and barcode specifications for your application.