Calculates the average amount of caffeine in a drink. The caffeine content of some drinks can differ substantially from the values given here. E.g. if you use twice as much coffee per water as usual, then your coffe of course will have twice the amount of caffeine. Different cola brands have different caffeine amounts. If you know the caffeine amount of a drink, rather enter the value yourself than using the average value given here. You can also enter your own contaier size.