Coffee stands as the most prevalent source of caffeine for adults, with an average 8-ounce cup containing approximately 95 milligrams of this stimulant. In moderate amounts, caffeine offers several benefits, including enhanced alertness, improved focus, and even better athletic performance.

The caffeine content in coffee is highly variable, influenced by factors such as the coffee type, preparation method, and even the brand. For popular coffee drinks, the average caffeine levels are as follows: brewed coffee typically contains 94.3 milligrams per 8-ounce serving, which can range from 113 to 247 mg in a 12-ounce serving. A single 1-ounce shot of espresso has about 62.8 mg of caffeine, while an 8-ounce cup of instant coffee provides 62.4 mg. Cold brew is notably stronger, offering 153–238 mg per 12-ounce serving. Even decaffeinated coffee is not entirely caffeine-free, usually containing around 2.4 mg per 8-ounce cup.

Several factors play a crucial role in determining the amount of caffeine present in your cup. The degree of roast is one such factor; light roast coffees generally have more caffeine, despite dark roasts often being perceived as stronger due to their bolder flavors. The type of coffee bean also matters significantly, as Robusta beans contain about 1.4 times more caffeine than Arabica beans. As mentioned, the type of coffee drink itself—be it espresso, cold brew, brewed, instant, or decaf—directly impacts caffeine levels. The origin of coffee beans can also influence caffeine content, with conventional beans potentially having more caffeine than organic ones. Water temperature during brewing affects extraction, with lower temperatures potentially reducing the amount of caffeine extracted. Furthermore, the coffee-to-water ratio is critical; a higher ratio of coffee grounds to water will result in a stronger drink with more caffeine per cup. Serving size is an obvious determinant, with larger servings like 12- or 16-ounce drinks naturally containing more total caffeine than a standard 8-ounce cup. Interestingly, contrary to a common misconception, brewing time does not appear to significantly affect the total amount of caffeine in coffee.

When it comes to safety, current guidelines suggest that most healthy adults should not exceed 400 milligrams of caffeine per day, which is equivalent to approximately four 8-ounce cups of brewed coffee. Exceeding this limit can lead to adverse side effects such as jitteriness, anxiety, sleep disturbances, or a rapid heartbeat. Pregnant individuals are advised to limit their caffeine intake to less than 200 milligrams daily, roughly equivalent to one 12-ounce cup of coffee. It is important to note that very large doses, around 1,200 milligrams of caffeine consumed at once, can lead to serious side effects, including seizures.