The average cup of coffee has around 100-120 mg of caffeine. The amount of caffeine in coffee depends on the type of bean, the roast, the brewing method, and how much water is used to create each brew. Generally speaking, Arabica beans contain less caffeine than Robusta beans. Darker roasts tend to have less caffeine than lighter roasts. And, brewing with more water (such as in a drip coffee maker) will result in a weaker cup of coffee with less caffeine.