Caffeine can vary greatly in a cup of coffee. Origins, blends, method of brewing, and the strength of the brew have to be taken into consideration. Also, instant coffee usually is less caffeinated than roast or ground. In the United States the measurement for a cup usually equals 6 ounces. Specifically, drip robusta coffees have from 140 – 200 mg caffeine per cup, about twice as much as arabicas which average about 75-130 mg. cup. Instant coffees are approximately 40-100 mg per cup.