Which is the best Keyword Density Percentage

Some of you may think this is so useless question But it's not, Bear with me on this.

I don't really focus much on keyword density but recently I noticed that some of my pages has 5%+ keyword dencity. When i wrote those pages I didn't even cared about this, but now i think it's important.

So can anyone of you tell me which the Golden number which i should keep in mind for keyword dencitry.