Caffeine content varies based on brewing method, tea or coffee type, and serving size. For estimation purposes, black tea contains approximately 60-65 mg of caffeine per 12 fl oz, while green tea has about 40-45 mg per 12 fl oz. Brewed black coffee typically contains around 140 mg of caffeine per 12 fl oz, and a single 1 fl oz shot of espresso has about 60-65 mg. Individual sensitivity to caffeine may vary, and consumption should be moderated accordingly.