Apple Watch uses the personal information you provide (age, gender, height, and weight) to help calculate a variety of metrics for your workouts and daily activity. It is important to enter and keep your weight accurate. (Don’t lie to your Apple Watch about your true weight!) Additionally, as Appel explained in a recent support document, you can calibrate your Apple Watch for even more accuracy.
You can calibrate your Apple Watch to improve the accuracy of your distance and pace measurements during walking or running workouts when GPS isn’t available (such as when you walk or run outdoors without your iPhone, or use a treadmill).
1. Bring your iPhone and your Apple Watch.
2. Find an open, flat area outside that offers good GPS reception and clear skies.
3. Make sure that Location Services is on. To check the setting on your iPhone, tap Settings > Privacy > Location Services.
4. Make sure that Motion Calibration & Distance is on. To check the setting on your iPhone, tap Settings > Privacy > Location Services > System Services.
5. Hold your iPhone in your hand, or attach it to your body with an armband (preferably) or waistband.
6. Open the Workout app on your Apple Watch, and choose Outdoor Walk or Outdoor Run.
7. Choose your goal, or select Open, and tap Start.
8. Walk or run at your normal pace for about 20 minutes.
If you can’t accumulate 20 minutes of outdoor walking or running during one Workout session, you can accumulate 20 minutes over multiple outdoor walking or running Workout sessions with your iPhone. If you frequently walk or run at a variety of different speeds, it’s best to accumulate 20 minutes of outdoor walking or running in the Workout app with your iPhone at each of the speeds at which you frequently walk or run.
You don’t need to do anything to start this calibration process. It can be done during a regular outdoor walking or running workout in the Workout app when you have your iPhone with you. And, whenever you use Apple Watch and iPhone to walk or run outside in the Workout app, it will continue to calibrate the accelerometer by learning your unique stride length at different speeds, and get more accurate over time.
This calibration process can also help improve the accuracy of your overall calorie estimations in many of the other workout categories in the Workout app, and the calorie, distance, Move, and Exercise estimations in the Activity app. However, it’s not necessary to do this calibration process before using either the Activity or Workout apps.
Note: Calibration data is stored locally on Apple Watch, and isn’t backed up to your iPhone. Therefore, your calibration data will be lost if you unpair your Apple Watch from your iPhone.