Fitbit inspire hr. is a friendly heart rate and fitness tracker for every day that helps you build healthy habits. This encouraging companion motivates you to reach your weight and fitness goals and even enjoy the journey with 24/7 heart rate, workout features, calorie burn tracking, goal celebrations, sleep stages and up to 5 days of battery life. Large fits wrist 7.1"" 8.7"" in circumference. Small fits wrist 5.5"" 7.1"".