For some reason and for many years there's a limit for font size in Illustrator. It is 1296 points max, so you can't go bigger without converting type to outlines first. Converting to outlines means you will not be able to edit type parameters and text it-self. Don't know how about you, but this makes me sad in non-destructive editing era.
What's your workaround?
The best workaround I found:
Now you can scale up text object to any size and keep it fully editable while font size is still 1296 pt. That's a good news, but the problem is that the text object it-self is still the same size it only appears bigger and if you'll hover the mouse pointer over it you'll see the actual size. Also if you'll switch to Outline view (Ctrl+Y) text object will appear without Transform... effect, so editing in Outline view becomes a guess work. And if you'll try to convert type to outlines you'll get actual 1296 pt size type outlined not the one you see. And that's where you can do the last try to fight the limits.
Now bounding box will become adequate to the text object size, text and type properties will still be fully editable, moreover now in Outline view you'll see the object as you see it in Preview. And even outlining type will now create outlines from what you see. Woah! Perfect workaround? Not really...
Very annoying drawback of this workaround is that each time you try to transform (move, rotate, reflect, scale, shear or align) the text object enlarged with Transform... effect, the effect immediately evaporates and text object become 1296 points size again.
How you can deal with it:
And here's another obvious option: as Cai mentioned, you can simply down-scale your whole document by 2 (or 3, or any number) and then increase document`s dpi by the same number. Cai gives an example: if your desirable document size is 3m x 1m at 150 dpi you can down-scale it to 1.5m x 0.5m, but use 300 dpi instead. Don't forget to mention this willful size mismatch if you share your project files with others.
A simple answer to your question is that you can create outlines from your text that are infinitely scaleable by pressing cmd+shift+o on a mac or ctrl+shift+o on a PC while your text is selected.
The real question is why are you needing a font that large in illustrator? You can design for billboards on a canvas that is only in the hundreds of points and still have a clear image. If you are dealing with images as well as vectors, I recommend using InDesign or Photoshop. That's what those were made for.
@Peacockerie, actually Photoshop was not made for type. Photoshop is a raster based program, while Illustrator is a vector based. Ultimately it should make type as large as necessary since it's essentially a mathematical equation between points. InDesign is a layout program so it is also not used for this. With 25+ years of graphic design as well as teaching, I am confident Illustrator should be able to do this, yet it isn't.
