Espresso has a lower volume of caffeine, but it definitely has a higher concentration. http://www.mayoclinic.com/print/caffeine/AN01211/METHOD=print http://www

Espresso has a lower volume of caffeine, but it definitely has a higher concentration. http://www.mayoclinic.com/print/caffeine/AN01211/METHOD=print http://www.mayoclinic.com/print/caffeine/AN01211/METHOD=prin... Espresso, restaurant-style 1 oz. (30 mL) 40-75 mg Generic brewed 8 oz. (240 mL) 95-200 mg The brewed coffee thus has between 11.9 mg and 25 mg of caffeine per oz. If you added a shot of espresso (let's assume the weakest one at 40 mg of caffeine) to an 8 oz of very strong coffee (at 200 mg of caffeine), you'd still be increasing the concentration to ~26.7 mg/oz. And that's stretching the limits of these calculations; a 200 mg 8 oz coffee is crazy strong, amounting to two and a half cans of Red Bull.