On average, an espresso contains around 63 milligrams of caffeine per ounce. Starbucks serves 75 milligrams of caffeine in each of its .75-ounce espresso shots. Dunkin Donuts claims a hefty 118 ...
A Tall Refresher has 35-45 milligrams of caffeine, while a Trenta contains 90-110 milligrams. For a bigger boost, Starbucks' Iced Energy Drinks offer up to 205 milligrams of caffeine.