The caffeine content in coffee varies depending on several factors, but on average, an 8-ounce cup of brewed coffee contains 80-100 mg of caffeine.
Here's a breakdown by coffee type:
Factors affecting caffeine levels include the type of coffee bean (Robusta has nearly twice the caffeine of Arabica), brewing method, serving size, and brewing time. A longer brewing time generally extracts more caffeine. For reference, the FDA suggests that 400 mg of caffeine per day is safe for most healthy adults, which equals about 4-5 cups of coffee.