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.