Using "ch" unit for limiting character count?

If I understand correctly the “CH” unit can be used to limit the amount of characters per line, where one CH equals roughly the width of one zero of the font used. So basically 20 CH would fit +/- 20 characters on a line before it breaks to the next line. While not super precise (some characters are wider or narrower than a zero) it’s very helpful as it is also kind of responsive.

Can the CH unit also be used to limit the amount of characters more generally, not just per line? I guess not. It looks like the CH value only deals with width.

What’s the best method to limit characters of a RTE CMS text?