Yeah, Bobby, you are right, the measuring is done by actual glyph measuring. This leads to the exact problem you assumed with the rounded stems with overshoots below the baseline — I learned it the hard way. Actually I hoped that Illustrator will grab the font data to set font height... but I now have doubts. If this information is available, why then the team decided to to the measuring instead? Only because these were the steps I demonstrated? I very much doubt. May be there is no such data in a font and I was wrong all along?

As for the alignment... There is a request for that, https://illustrator.uservoice.com/forums/333657/suggestions/41485519
You commented for it, but never voted. Please do, every voice matters. It’d be great if you also voted for other request.

For the most part the font height options feature is pretty well implemented. Illustrator's developers have had to split the difference between using the physical size of characters and a font file's built in dimensions.

A conventional sans serif face like Gotham will have its physical features line up precisely with the horizontal guide lines for baseline, cap height and x-height. Then there are other typefaces whose capitals don't reach the cap height line. Some serif text faces do this and it is a common feature with many script faces. If Illustrator only based its cap height setting on the distance between baseline and cap height line the letters in some typefaces would end up being under-sized. I guess I'm not surprised there would be an issue with rounded letter forms.

There is another type-related feature I desperately want added: aligning the baseline of text objects with other objects, be it a geometrical shape or another type object. Right now I have to manually move the objects in order to have the text baseline "snapped" to something else. It would be far more simple (and much faster) to be able to select a text object, a target object and then click an alignment button (or keyboard shortcut) to auto-align via baseline. It's worth mentioning some rival applications do allow baseline alignment, even with multi-line strings or blocks of text (with first baseline or last baseline alignment).

Regarding previous comment, in recent version Illustrator does remember which part of a text had which option chosen. That is fixed.

The setting doesn’t stick to a text object. After the application is restarted (or even document is reopened), it falls back to Em Box for each one of them :( This is not convenient.

Don’t forget to include these to Paragraph and Character Styles windows, please.

The space is missing in the 'Default (Em Box)' option in the Font Height drop-down menu in Character panel

Please add custom-assignable hotkeys for these commands (in 'Other Text' section, blank by default):
— Highlight font height using Default (Em Box)
— Highlight font height using Cap-Height
— Highlight font height using x-Height
— Highlight font height using ICF box
So pressing a hotkey would change the 'Font Height' option to the chosen one and then set the cursor to the 'Font Size' field.
This would allow to quickly set the height by the option needed from the keyboard, without changing it with the mouse.

I agree with some here that illustrator lacks some very crucial features, If I want 20mm letters (cap ht) I should be able to type 20mm into the field, as with Flexisign, But by far the most important feature missing is the ability to smooth a curve, in Flexi you choose 2 points anywhere on a curve, no matter how many nodes are in between the two points and hit return and the entire curve is smoothed to a perfect mathematical shape with bezier handles for precision adjustment. I struggle to draw in AI and will always resort back to Flexi to achieve perfection It's 10x better for vector drawing,,,Even though Flexi is a now the shadow of the program it once was, now that it is PC only (no mac available)

Adobe Illustrator, before printing die cut, click and check Font size is height is 9.5cm, after printing die cut after size is 5.5cm......
Zzzz double check font size correct print (pls don't show me the wrong correct font size) = cut your salary
After die cut wrong size check the Font must create outlines check (size is 5.5cm),
NOOOOOOOO my boss say want to cut my salary..........

There's a script that helps with setting both x-height and cap height.
http://illustrator.hilfdirselbst.ch/dokuwiki/en/skripte/javascript/uebersicht
Search for WR-capitalSize and then modify it to use any symbol you want.
Still it's much needed thing in AI from the box.

In the food pack world, there are indeed local guidelines when it comes to x height and that would be a game changer to be able to do so easily!

In the signage world Character Height is critical as much of the time this is regulated by Federal or Local guidelines. Though, for some reason, Adobe Illustrator does not allow one to simply choose the font size and have it be the specified character height rather each font is a different size. I also use Auto CAD for design purposes and that program does not have the issue with character height.

Adobe is a lot nicer program for doing proof overlays on photos than CAD though if my text is incorrect size than it doesn't matter. I have seen forums since 2012 looking for a simple fix yet there still is none.

very useful

Illustrator is one of the WORST programs for setting type that I have used since starting in 1988. Also one of the worst for editing points. Complete **** for a sign shop.

Can someone advise on the answer to this? I am having the same trouble.

Sorry, I found your big comment in other request, you seem to already know about these scripts.
I totally agree about UPM and other dimensions all fonts already have, and AI's inability to give access to them.
I would also like to have these sizes to be visible as guides when using Smart guides for a live text.

Bobby, I can advise using scripts that set cap-height and x-height, based on measuring actual outlines of specified letters, by Wolfgang's Reszel.
Again :)
Voted

For sign design work and creating graphics for LED-based signs it's crucial to be able to size, position and align type objects according to capital letter height. Adobe Illustrator currently has no features to support this kind of work, which forces me to hop back and forth to other programs (like CorelDRAW and Flexi) that directly support those features or have work-arounds that won't drive designers crazy.

Illustrator's type functions are still confined to the paradigm of setting type for the printed page. If I want lettering whose capitals are exactly 20 pixels tall for display on a LED jumbotron Adobe Illustrator will not deliver that. It sizes that blue box around the lettering to 20 pixels, not the actual capitals -which makes the lettering even more fuzzy. I'm trying to at least have the cap line and base line hit that pixel grid exactly. The same problem exists in physical lettering used on signs, be it 24 inch tall channel letters on a building sign for 1.5" tall letters on a door graphic. You can't size those objects exactly without a bunch of time-consuming work arounds. And then for something very basic, aligning a text object over the center or a box or some other container, Adobe Illustrator won't deliver the correct result, aligning the text according to the capital letter. Instead, if you align a text object over another container the text object is placed too high and you have to manually correct the error. It's very frustrating.

When I enter Helvetica and size it to 6 inches, the font produced is only 4 inches. When I type in a letter size, I want that size, Adobe seems to add part of the base line to the font size.

So, one problem is that not all fonts cover the same writing systems. If you have your prefs set to "cap height" what happens to fonts installed on your computer that literally do not have capital letters? Symbolic fonts, non-western fonts that skipped even basic Latin, and others. This is one reason Adobe hasn't yet done this: because these corner cases exist on almost every user's computer, and make the problem more complex.

The existing point systems is awful... except for all the alternatives.