Thickness and positioning of text underline

Question

I previously asked a technical question on StackOverflow about getting the thickness of the underline from a font in Java/Android. Since it is starting to appear that there may not be a solution, my new problem becomes: how do I design a good underline thickness and position for any particular font size?

The following image is an example:

The red lines show the top, baseline, and bottom of the font. The black line is a standard underline. If that black line didn't exist and I had to design it myself, how would I know how thick to make it? And how far should it be placed below the baseline?

Just by analyzing the image it looks like the thickness is about 1/16th of the font height and about one line thickness below the baseline. Is this a good guideline? I'm sure there must be design standards or at least recommendations out there, but I wasn't able to find them.

Answer 1

I am not sure if there's a straight forward way of calculating this (I hope that if anyone else here knows the contrary to correct me). Most go with what looks best.

I also don't thing the height of the font has anything to do with this, more likely the stroke weight of the letters themselves. For a basic rule I saw many using, keep the stroke thinner than the font's stroke weight. Other than that, do what looks best for your designs.

PS: In your example, the underline has a weight of 2/3 of the font weight. Why not start from there?