How much weight is on the bar - Weightlifting question?

I have a question about weightlifting. Example: I have a bar bell, and I put one 10lb plate on one end, and other 10lb plate on the other end. Does this equal 10lbs, or 20lbs? Same goes with small and large bars. I guess I'm wondering because I want to know if I'm curling 10lbs or 20lbs, and I'm not sure! Thanks!|||it equals 20lbs.