Symptoms

It may happen that the font size changes unexpectedly for some text in a label design when using a different printer than the one specified when designing the template. 

Diagnosis

This may happen because the new printer has a different DPI than the one specified originally. 

The reason for this is that Fonts are measured in point sizes which don't correspond directly to the printer dots used by the printer to draw individual characters. This means that changing resolution(i.e.: number of dots) at which characters are printed may change the space that a character occupies at a particular point size. 

Find below an example of how font size is calculated:

• Points correspond to 1/72 of an inch meaning an 8 point font corresponds to 8/72 of an inch.
• When switching from 600 dpi to a 300 dpi the number of dots changes: At 600 dpi, this would result in 66.667 dots, which gets rounded up to 67 dots. At 300 dpi, this would result in 33.333 dots, which would get rounded down to 33 dots.
• Note that because 300 and 600 are not multiples of 72 the number of dots used for 600 dpi is not exactly double the number of dots used for 300 dpi
• This causes the font to render larger on a 600 dpi printer. This cannot be fixed, because a 300 dpi printer is actually incapable of rendering a font at exactly 8 pt due to its low resolution.

Solution

As illustrated by the example above font size changes in these instances are a defined behavior that is not really fixable.