I don't know the exact #, but I can say this: I started out with a beautiful and great expository on why I wanted to be a doc, it was probably 1.5 pages single space 10 pt. But by the time I was done with the online app, it had been slashed to half it's original size. Eeeeek. Good luck!
I don't remember how many characters/words were *allowed*, but I really played around with mine in the online app until it fit. You can always substitute shorter words for longer ones so that you don't have to cut too much content. It may not be as elloquent, but it will still get your point across.