ZPL at 203 dpi vs 300 dpi

ZPL coordinates are in dots, so the same ZPL prints about a third smaller on a 300 dpi printer than on a 203 dpi one: 12 dots per millimetre instead of 8. Either rewrite the coordinates for the new density or add ^MUD,200,300 at the start of the label to scale them.

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

Same ZPL, two printers

The box below is 560 dots wide in both renders. At 203 dpi that is 70 mm; at 300 dpi it is 46.7 mm, because each dot is smaller. The label is 4 × 2 in in both.

8 dpmm (203 dpi)

^XA
^FO20,20^GB560,200,4^FS
^FO40,50^A0N,50,50^FDSame ZPL^FS
^FO40,120^A0N,30,30^FD560 x 200 dots box^FS
^XZ

12 dpmm (300 dpi)

^XA
^FO20,20^GB560,200,4^FS
^FO40,50^A0N,50,50^FDSame ZPL^FS
^FO40,120^A0N,30,30^FD560 x 200 dots box^FS
^XZ

Exact densities

Printers are named by rounded dpi, but they are built in dots per millimetre (dpmm), and the OpenZPL API, like Labelary's, takes dpmm. The exact dpi is dpmm × 25.4:

So "300 dpi" is really 304.8. Computing dots with 300 instead of 304.8 drifts by 1.6%: 29 dots across a 6 in label.

Label sizes in dots

Dots = millimetres × dpmm, from the exact density. ^PW and ^LL take whole dots, so round down:

The size of the rendered image

The image the API returns follows a different rule, the same one Labelary uses: it counts whole dpi, 152, 203, 304 or 609 (dpmm × 25.4, rounded down), and multiplies them by the size in inches, rounding down again. So a 4 × 6 in label at 8 dpmm comes back as 812 × 1218 pixels, and at 12 dpmm as 1216 × 1824, slightly fewer than the physical dots above. Measured on the engine:

One dot is one pixel, so a layout that uses every dot of the first table can lose its last row or column in the image: with ^LL1219 on a 4 × 6 in label at 8 dpmm, dot row 1218 falls outside the 1218-pixel image (rows 0 to 1217). Keep a margin of a few dots at the edges.

The label size pages have more sizes and a calculator.

Fix 1: scale the label with ^MU

^MUD,200,300 tells the printer the coordinates were written for 200 dpi and should be scaled to 300. Put it right after ^XA. In the OpenZPL engine it multiplies positions, boxes and font sizes by 1.5, and the box is back to its 203 dpi size:

12 dpmm, no ^MU

^XA
^FO20,20^GB560,200,4^FS
^FO40,50^A0N,50,50^FDSame ZPL^FS
^FO40,120^A0N,30,30^FD560 x 200 dots box^FS
^XZ

12 dpmm with ^MUD,200,300

^XA
^MUD,200,300
^FO20,20^GB560,200,4^FS
^FO40,50^A0N,50,50^FDSame ZPL^FS
^FO40,120^A0N,30,30^FD560 x 200 dots box^FS
^XZ

It's the quickest fix for a carrier label written for 203 dpi. Check barcodes after scaling: bar widths are whole dots, and the printer has to round them.

Fix 2: rewrite the coordinates

For a label you maintain, generate it for the target density: multiply every position, size and font height by 12 / 8 = 1.5 for 203 → 300 dpi, and set ^PW and ^LL from the table above. Or work in millimetres: with ^MUM every following coordinate is in millimetres and the label keeps its physical size on any density.

Which density should I choose?

• 203 dpi is the default for shipping labels: carriers generate ZPL for it, and their barcodes are sized for it.
• 300 dpi pays off for small labels, small text (under about 6 pt) and dense 2D codes, such as jewellery tags or electronic component labels.
• 600 dpi is for very small labels and fine print; its printheads cost more and wear faster.

To find your printer's density, print a configuration label (usually by holding the feed button) and look for the resolution, or read it in the printer's web page. Then preview with the same density in the viewer.