It's easy to try and second guess the preferences of the admissions officers who will be reading your college application. The instructions on the Common Application state that the Short Answer has a "1,000 character limit." Does this mean that fewer is better? Will the admissions folks appreciate brevity? Or is 1,000 characters simply a suggestion, and a Short Answer of 1,200 characters really isn't a problem?
First of all, realize that the admissions officers don't count words or characters. If your short answer is 900 characters or 950 characters, no one is really going to notice or care. However, the 1,000 character limit is firm. The online Common Application will return an error if you go over 1,000 characters, and the downloadable and printable version has space for no more than about 1,000 characters.
Up until 2011, the guidelines said the essay should be "150 words or fewer." The new 1,000 character guidelines can lead to an essay that is a little longer than 150 words. My recommendation (and some counselors disagree with me) is to continue to shoot for something in the 150 word range. As for brevity, 150 words is already very short. At 150 words your answer will be a single paragraph that the person reviewing applications can read in less than a minute. My advice here is to not try to go too short. Can you really say anything meaningful about your work or an extracurricular in 75 words? The instructions tell you to "elaborate" on one of your activities, and anything much less than 150 words isn't much space in which to elaborate.
So what is the ideal Short Answer length? You can't go beyond 1,000 characters, but I'd recommend landing in the 750 to 1,000 character range. Stick to the directions and make sure you say something meaningful about one of your activities.