The caffeine content in coffee drinks can fluctuate slightly due to various factors such as the depth of roast, how finely the coffee is ground, as well as how long it is brewed. The caffeine content of tea also vacillates depending on how long it is brewed. Surprisingly, lighter roasts contain more caffeine due to the beans’ higher density, and espresso has a lower caffeine content than brewed coffee due to how quickly the water passes through the grind, and is expelled.

Coffee:

Brewed 8 oz. (237 ml) 95-200 mg 

Espresso 1 oz. (30 ml) 47-75 mg

Instant 8 oz. (237 ml) 27-173 mg

Tea:

Black tea 8 oz. (237 ml) 14-70 mg

Oolong tea 8 oz. (237 ml) 50-75 mg

White tea 8 oz. (237 ml) 30-55 mg

Green tea 8 oz. (237 ml) 24-45 mg

*caffeine is listed in mg

http://www.mayoclinic.org/healthy-lifestyle/nutrition-and-healthy-eating/in-depth/caffeine/art-20049372