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.

Updated 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.