What About Espresso?
Espresso is another matter altogether, since it is brewed differently than coffee and not usually enjoyed in 8-oz cups. An average shot of espresso has around 30 to 50 mg of caffeine, which is definitely less than what you get in a cup of coffee. But a shot of espresso is only 1-oz in volume. So if you wanted to compare 1 shot of espresso with 1 cup of coffee, then the coffee definitely has more caffeine. But ounce for ounce, espresso is the one with the bigger caffeine punch. And the caffeine content for different roasts does still apply, except that nobody makes espresso with lightly roasted coffee beans. There is a reason why dark beans are actually called Espresso roasted, so you aren't really going to have to worry about any differences in this case.