dpi (dots per inch) on label printers

dpi is the number of dots a printhead prints per inch. Label printers are sold as 152, 203, 300 or 600 dpi, which are rounded names for 6, 8, 12 and 24 dots per millimetre.

Aktualisiert am 2026-10-20 · Renders made with the OpenZPL engine

The names are rounded

Zebra printheads are built in dots per millimetre. Converted exactly, 8 dpmm is 203.2 dpi and 12 dpmm is 304.8 dpi, not 300. The commercial names round the number; the dots on paper follow the dpmm value.

Why the difference matters

If you compute a 4 in label at "300 dpi" you get 1,200 dots; at the real 304.8 dpi it is 1,219 dots. A ^PW of 1200 leaves about 1.6 mm unused on the right. On a 6 in label the gap is close to 2.4 mm, enough to cut off a right-aligned field.

Renderers use a whole number of dpi for the image size. Labelary and the OpenZPL API size a 4 × 6 in label at 8 dpmm as 812 × 1218 px: 203 whole dpi times the inches, rounded down (tested on both 2026-10-20). At 12 dpmm that is 304 dpi, 1216 × 1824 px. This changes only the last rows and columns of the image, never where a field lands.

dpi or dpmm?

Use dpi to talk about the printer you buy; use dpmm for arithmetic and for the API URL. Higher dpi means smaller dots: sharper small text and denser 2D codes, but the same ZPL prints smaller, so a template made for 203 dpi needs scaling for 300 dpi.