8 energy drinks, ranked by caffeine per serving as sold, straight from each brand's own nutrition panel or official website. Can size varies as much as strength does, so two drinks with the same caffeine per ounce can differ a lot per can.

Energy drinks are one of the easiest ways to blow past a daily limit without noticing, since several pack more than a strong cup of coffee. Add today's cans to the caffeine calculator to see where you stand.