Print calibration

Why labels come out small

Almost every browser, PDF reader and printer driver defaults to fitting the page into the printer's imageable area. A physical printer cannot print to the edge of the paper, so “fit to page” shrinks the content by whatever margin the hardware needs — typically 2 to 6 percent.

Two percent on a 25.4 mm label is half a millimetre. That is enough to make a label stop wrapping a cryovial, and it is invisible unless you measure. Nothing about the file is wrong; the scaling happened downstream of it.

Get the calibration sheet

One page with a 100 mm rule across, a 100 mm rule down and a 25 mm square. It is written in your browser and never sent anywhere.

Calibrating in four steps

1. Print the sheet at 100%Set scaling to 100% or Actual Size in the print dialog — not Fit, not Shrink to Fit, not Auto. The sheet carries a 100 mm rule in each direction, because a printer can be honest across and wrong down.
2. Measure the 100 mm ruleUse a steel rule if you have one. Measure the printed 100 mm line and note what it actually reads.
3. Compute the scaleMeasured ÷ 100 is the scale factor your path is applying. 98 mm means 98%; the labels are 2% small.
4. Fix it at the sourceTurn off fit-to-page and reprint. If your driver has no 100% option, the scale factor tells you what compensating size to enter — but a driver that cannot print at true size is the wrong path for exact-size work.

What the editor does to keep output honest

One canonical geometry

The preview, the browser print and the PDF are all drawn from the same scene in integer micrometres. There is no separate print layout to drift out of step.

Exact page sizes

Thermal output writes a PDF page the exact size of the label, so there is no page for a driver to fit the label into.

Real millimetres in the browser

The print surface is laid out in physical millimetre units, not pixels, so the browser's own scaling is the only variable left.

Clipping is blocked, not hidden

Content that will not fit inside the label is a blocking error before output, with the exact size it needs. Nothing is shrunk to make it fit.