This question is interesting. So we can easily know whether or not we are overdoing our daily caffeine dose. It depends a lot on how we prepare the coffee:

Drip Coffee:

a cup of brewed coffee (24cl) contains approximately 70-140 mg of caffeine

Espresso:

A 30-50 ml cup of espresso contains approximately 63 mg of caffeine.

Instant Coffee:

contains less caffeine, about 30-80mg (one or two tablespoons of coffee)
Decaffeinated coffee: contains less than 10mg of caffeine per cup.

And what will be the degree of caffeine if you go to Starbucks for a cup of coffee:

Short: 180 mg caffeine

Tall: 260mg caffeine

Large: 330 mg caffeine

Venti: 415 mg of caffeine