A typical cup of coffee (6-8 ounces) contains approximately 100mg to 300mg of caffeine, potentially reaching 400-500mg if brewed very strong or with added espresso.

“But we can set some outer bounds on the total amount of caffeine that likely exists in a cup of coffee, and it's probably somewhere between 100 milligrams-- that would be on the weaker side for a six or eight ounce cup of coffee-- out to about 300 milligrams for the equivalent six to eight ounces of coffee. But if you were to brew your coffee very, very strong or, like me, occasionally throw a shot of espresso in there, too, you could get that number up to 400 or 500 milligrams of caffeine.”