For years I've been making feature requests to the Illustrator team to provide the option to size, position and align type in reference to the capital letter height of a type object. Some of my more recent requests (with illustrated examples) seem to have been flushed with the changes made to this user request forum. This would be very useful for sign design purposes and any other project where absolute cap letter height specification is needed. For instance, I create a lot of graphics for LED-based variable message center signs. Type tends to look a lot better when the baseline and cap height line of letters corresponds to the pixel grid of the LED display. For instance if I make cap letters exactly 20 pixels tall they're going to look sharper while letters 19.47 pixels tall are going to look fuzzy in all directions.

All fonts have built-in numerical values for dimensions, such as overall UPM size, ascender, descender, cap height and lowercase x-height. For example Gotham Book has an overall UPM size of 1000, ascender is 800, descender is -200, cap height is 700 and x-height is 517.

What I find strange is the blue box Illustrator puts around all type objects doesn't correspond at all to the UPM size of a letter. If I type a capital "E" in Gotham Book, size that blue box to 1 inch tall, the "E" should come out to .7" when converted to outlines, right? No, it comes out to .6398" tall.

I'm not asking Adobe to replace traditional type layout standards with this approach. People who are used to setting type on the printed page, thinking in terms of baseline grids and distance from one baseline to the next get pretty defensive whenever this suggestion is made. "That's not how type works," is the common retort. When you're doing sign design or setting type in other kinds of mediums the baseline grid approach just doesn't work. You have to go by what you can actually see: physical letter sizes and distance between those letters.

In regards to various scripts that reference M-height or x-height and scale letters accordingly, that approach only works with typefaces whose squared off letters align perfectly with the baseline and cap height line. Clean, sans serif typefaces like Helvetica and Gotham work alright with that system. The scripts don't work well with many decorative typefaces and script typefaces. That's where using the font file's internal dimensions becomes critical for accurate sizing, position and alignment. Like if I want to set Sloop Script with 2" tall letters and vertically center it in a 3" tall box I'm not going to be able to do that even with the various letter sizing scripts out there.

I too need real sizes in my sign making business. When I want a 6 inch letter I want it to be 6 inches not 4 inches. Other sign making programs can make fonts appear in real sizes. This should be an option. I noticed that the font size in Illustrator is the letter height plus the space underneath the letter to the top of the next letter. Please give us an option for actual letter sizes.

I guess you have never these pictures:
https://i.stack.imgur.com/ntg5f.png
You seem to not knowing much about things you do. 'Print size'? What kind of ignoramus are you? Fonts are much more complicated than your understanding of it.
But the problem is still there. I have scripts, based on Wolfgang's Reszel scripts, to set x-height and cap-height (and digit size, which is frequently different from a cap-height), based on realtime measurement of height of 'z' and 'Z' outlines (as common 'flat-surfaced' letters), but there would be so much profit if AI could allow to measure and set these, based on values included into font itself.

This is a huge problem for my workflow. I need real sizes, not "print" sizes. Pick a letter, like the H. Make the measurement based on that. Maybe make it an option as I'm sure there is a reason that it is the way it is now, even if I can't find a use for it.

When you type and than select a text/number on the screen to see the size, the measure box shows for example in "cm" the hight of the text. When you measure the same text/numbers after printing the result is a lot different (smaller) than the measurement on the screen showed. For example a number of 15cm is after printing only 9,4cm.

Correct the size of the fonts in the navigator info box to the real size measurements as the print results.

When you type and than select a text/number on the screen to see the size, the measure box shows for example in "cm" the hight of the text. When you measure the same text/numbers after printing the result is a lot different (smaller) than the measurement on the screen showed. For example a number of 15cm is after printing only 9,4cm.
I use the Illustrator CC 2017.1.0 version, but also the C5 has this problem.

Greatings,