The most common way that I used to throw knives was by holding onto the blade and throwing like a baseball. So I'd estimate that at three or four yards it would be a half a turn, and whatever that distance it would be multiplied by three for 1 1/2 turns, although in practice maybe a bit less.
At close distances you can also let the knife slide out of your hand, and I've seen that technique once in a movie, but the other way is better, anyway, in a real fight throwing a weapon at someone just seems like a bad idea, and you'd be better off holding onto it in my opinion.