The caffeine content in a cup of coffee varies depending on factors such as the type of coffee bean, brewing method, serving size, and roast. However, general estimates are as follows:

• A standard 8-ounce (about 240 ml) cup of brewed coffee typically contains around 95 mg of caffeine, though it can range from about 70 mg to 140 mg depending on preparation and coffee-to-water ratio

• A 12-ounce cup of brewed coffee may contain approximately 113 to 247 mg of caffeine, according to the U.S. FDA

• Espresso, which is more concentrated, contains about 63 mg of caffeine per 1-ounce shot, but since espresso-based drinks vary in size, total caffeine depends on the number of shots used

• The caffeine content also depends on the coffee bean species: Robusta beans have about twice the caffeine of Arabica beans

• Factors like grind size and brewing time affect caffeine extraction; finer grounds and longer contact with water increase caffeine content

In summary, an average cup of brewed coffee has roughly 95 mg of caffeine, but this can vary widely based on many factors.