I'm trying to limit instructional text in a form.
Can I shorten "75 characters" to "75 chars" and have it be clear to a fairly inexperienced Web user?
Yes, but there's a nicer way to do it.
Case in point: composing a tweet in Twitter, which has a limit of 140 characters.
Quite simply there is a number by the submit button in clear view that shows the number of remaining characters that decreases as you type, and once the user exceeds the limit the submit button is disabled and the negative remaining characters label is now red.
The character limit is then almost implicit without requiring that the user has read or understood that there is a limit in place.
It depends on what you call "universal"... In French, "char" is a name, and might mean a chariot, a tank, etc. :-) This abbreviation talks probably to most programmers, but I am unsure about the average pedestrian.
It's definitely not a common abbreviation for a general population audience. Instead, I'm wondering why you want to display this information at all to the default user. You say this is for a field for the user to enter his title. Most likely that will be a very short entry and he will never get even near your 75 word limitation.
So the proper solution would be to display a warning once she reaches something like 65 characters.
Using Twitter's pattern (of showing a character countdown from 75 on downwards) is out of place here because it's not useful for the user to know about it. With my solution you don't bother 90% of the users with useless information but you also offer a useful explanation to those users that actually hit the limitation.
I know the abbreviation is very common universally with programmers but i don't think it is half as common with users in general. I would set up an online poll or something like that and asks friends, family etc what they would associate char with then get the results and make a decision based on the results.
How about "letters" as an alternative? Its shorter than "characters" yet more commonly understandable.
Edit: or "signs", to also include punctuation.