Render text same size regardless of resolution.

I would like to render UI text the same size in my game regardless of what resolution the game is running at. So if the user is playing at 800*600, the text should take up the same amount of monitor space as it would at 1920x1040 or something, but look less appealing. I tried to look for SVG fonts or something, but didn’t find any.
I guess i could use freetype and have higher font sizes for higher resolutions, but i wouldn’t really know what font size to use for what resolution.