Occasionally I get asked if there is a way to define the actual letter-height instead of the slug-heigt.

Only if you know the proportions of e.g. cap-height to slug-height and enter something like "12pt * 0.671". That's obviously a bother since you first have to find out that proportion.

A script can do the maths for you, as usual.

It does so by converting a userdefined character to outlines and measuring the size before and after. By letting the user decide which character to outline it is possible to define the x-height as well as the cap-height.

As with other formatting options it does not matter if you have text selected or text frames. The Script will handle both.

If this is the situation to start with:

Then these values...

...result in this

The ‚G‘ is the same size in all frame i.e. 5mm.These values:

bring all "e" to be 5mm.