SVG document units and font size in Inkscape?

Question

Using Inkscape 1.2:

• I start a new blank document
• File / Document properties; I first change Display units to pt; then change Front page: Format: Custom pt; I get scale 2.834646 as Scale (pt per user unit)
  • (so ... now I have 1 pt = 2.834646 ... pt ??)
• Then I add text; at the top bar, I set its font size to 12 (apparently) pt - but if observed in Selectors and CSS, the font-size attribute of this text ends up as 4.23333px (and definitely style="...;font-size:4.23333px;..." ends up the svg as well)??!

So, what is the logic behind specifying font size of 12 pt as 4.23333px in SVG, when the document unit is set to pt?! How did Inkscape arrive at 4.23333px from the original 12pt ?

Answer 1

You have to set the document 'Scale' to 1 pt per user unit, after changing the canvas dimension units, to actually adjust the coordinate system inside the file. The '4.23333px' is still relative to the previous units the document was scaled to.

The font size is always saved as 'px' (there is some code in Inkscape's source related to an option allowing 'font-size' to be saved as other units, but it's commented out, so there is no way to enable this behavior). However, after setting the scale, all numbers with the 'px'-suffix or without a suffix (meaning "user units") equal pt.