I use so much stevia its ridiculous. 2 4oz bottles a week.
Just be sure you get the liquid and not that powdered crap like Stevia in the raw or Truvia. Because while the stevia has no calories, the bulking agent, which is usually maltodextrin or dextrose, does. Every packet has like... 3.5 calories. The fda says anything under 5 calories a serving is calorie free. So that's how they get away with it. But I found myself jhaving to use about 9 packets at a time just to sweeten a glass of tea.