I’ve tested hundreds of smartwatches: here’s what the most common metrics mean

Smartwatches measure more health and fitness metrics than ever before. These metrics can help users track everything from steps to SpO2 and provide important insights. At least, if you understand what they mean. Learn about the most common smartwatch metrics you can find on your device.

Most devices track at least a basic level of activity data to help users assess their daily movements. These statistics largely speak for themselves.

• Steps: Your step count is literally the number of steps you take. Calculating this measurable number behind the scenes usually involves an accelerometer and a gyroscope.
• Floors climbed: An altimeter is required to calculate the floors climbed. On average, wearables calculate a height difference of approximately 3 meters per floor.
• Calories burned: This statistic represents the calories your body has burned through physical activity. This is more than the number of calories burned at rest due to typical physiological functions.
• Activity/exercise: Some platforms also provide a measure of minutes of daily activity based on recorded workouts or increased heart rate indicating activity. On the Apple Watch, for example, this is shown by the green exercise ring.

Many smartwatches are actually quite powerful fitness trackers. The most popular devices record workouts, GPS routes, and even details related to specific activity types, such as a runner’s pace and cadence or a swimmer’s laps. To find out what your device has to offer, you can consult the corresponding app on your smartphone.

Depending on your wearable, sleep tracking can include a wide range of metrics or just some basic data. Below are the most common and useful ones.

• Time in bed: This includes the total time from the moment the device detects that you have gotten into bed to the moment you get out. This can include activities such as reading in bed, but also periods of being awake during the night. This metric can help users identify discrepancies between the amount of time they think they spend sleeping and how much they actually sleep.
• Total sleep: Total sleep is the complete measure of actual sleep time. Some wearables also offer sleep efficiency measurement.
• Sleep stages: Each sleep phase, Light, Deep and REM, coincides with specific brain wave and neuronal activity patterns and plays a specific role in recovery processes. The phases are identified by changes in heart rate, heart rate variability, and breathing patterns.
• Respiratory rate: Respiratory rate, or breathing rate, is measured during the night to detect signs of a serious illness such as sleep apnea. According to the National Institute of Health, a normal breathing rate for adults is about 12 to 20 breaths per minute.
• Temperature: Monitoring temperatures at night has also become increasingly popular. Monitoring even subtle changes in body temperature can help you detect early signs of illness or ailments. It is also very useful in tracking women’s health.

Heart rate is at the heart of tracking your health. It’s so important that some devices, like the Oura Ring, rely almost exclusively on the measurement. Heart rate data shows everything from fitness to stress levels and overall health. Some devices also provide high/low or irregular heart rate notifications.

• Resting heart rate: Just like it sounds, resting heart rate is the number of beats per minute your heart experiences when you are sitting or lying down. For most adults, a healthy range is between 60 and 100 beats per minute. Most wearables also measure users’ resting heart rate during the night, which can average closer to 40 to 50 beats per minute.
• Active heart rate: Active heart rate is the same measurement, but during exercise. Depending on your age, fitness level and the intensity of your activity, your active heart rate may be much higher than your resting heart rate. Many platforms help users set target heart rate zones to guide workouts.
• Heart rate variability: HRV, a measurement of the variation in time between heartbeats, indicates your physical health and can highlight problems such as heart disease or indicate cardiovascular fitness. Factors that influence HRV include stress, sleep, diet, physical fitness and exercise.

Some devices also provide ECG measurements on demand. This is a non-invasive test for measuring the electrical activity of your heart that can be used to detect abnormal rhythms and signs of heart disease and other heart conditions.

Blood oxygen is the measurement of hemoglobin in your red blood cells, which transport oxygen throughout the body. The average healthy person maintains blood oxygen levels between 95 and 100%. Many popular devices provide SpO2 averages and measurements on demand.

Some devices also offer a VO2 max measurement that indicates how much oxygen your body absorbs during exercise (V for volume). VO2 max is a useful indicator of cardiovascular health and aerobic fitness. A high reading means that your heart is effectively supplying blood to your muscles.