Specify the scaling of a staff in millimeters?

For the printout, I want to specify the scaling of a staff, i.e. the height of the 5 lines in millimeters.
Where can I specify this?

I think you’re looking for the staff size, which by default is set in spaces in Dorico. You can change your default unit of measurement for various options, but I can’t remember if that shows the staff size in that unit or always in spaces though.

It’s in Preferences, and yes, space size will show in mm (logically, as a space will always be a space!).

Thanks, learned something again. I will have a look at the matter.

I have now tried setting the spatia setting to 4mm. When printing, I get a staff with 5mm total height instead of 16mm. When I specify 8mm spatium, I get 9.7mm total height. (the correct printer driver etc.)
When I export the output as SVG I also get completely different values that have nothing to do with my inputs. Is there a scaling factor somewhere else that I should include?

No, there’s no “hidden” extra scaling to account for unless you’ve done it explicitly. One of the things I love about Dorico as opposed to Finale. Are you printing to “fit to page”?

Or, have you re-sized the staves manually to a percentage? That would be Edit Menu–Staff Size.

When you export graphic to PDF, can you check the PDF in a PDF reader that includes a ruler, to confirm the “absolute” size?

One more question, forgive the obvious possibility: have you confirmed you’re exporting and viewing the intended layout?

There’s the possibility of setting the space size to something different at any system break or page break, in addition to the Staff Size menu option that Dan’s mentioned.

It’s also possible that you’ve e.g. set Layout Options to use a page size of A3 but are actually printing to e.g. 2Ups on A4 (which would actually mean a page size of A5, a quarter or A3).

I think I understand things a little better now.
I will investigate this in more detail tomorrow.
But as far as I can see, it has to do with the fitting of the page.
However, I’m just wondering how I could output a PNG with a page width that I specify.
Right now I only see the possibilities of the system specified page sizes and widths that are preset for printers. Or I also don’t know how I could specify the output size for an SVG.

When you output a graphic, it outputs according to the dimensions of your selected layout.

If you’re trying to output a PNG of a fixed width without any margins, you’ll need to specify the page margins to be zero in Layout Options.