Caffeine is naturally occurring in over 60 types of plant species; the most common being coffee Arabica and coffee Robusta, tea and cocoa beans.
Cup sizes vary considerably across Europe. As a guideline a 150 ml sized cup from ground roasted coffee Arabica contains around 85 mg, instant coffee 60 mg, decaffeinated coffee 3 mg, leaf or bag tea 30 mg, instant tea 20 mg and cocoa or hot chocolate 4 mg caffeine.
Robusta coffees have about twice as much caffeine as Arabica coffees.
Decaffeinated green coffee must contain less than 0.1% caffeine (dry weight) to comply with EU regulations. This corresponds to about 3 mg caffeine in a cup of decaffeinated coffee.