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You can calibrate your Apple Watch to improve the accuracy of your distance and pace measurements when GPS isn't available. For example, when you walk or run on a treadmill or outdoors without your iPhone.

Calibrate your Apple Watch
- Bring your iPhone and Apple Watch to a flat, open, outdoor area that offers good GPS reception and clear skies.
- Check that Location Services is turned on. On your iPhone, tap Settings > Privacy > Location Services.
- Check that Motion Calibration & Distance is turned on. On your iPhone, tap Settings > Privacy > Location Services > System Services.
- Hold your iPhone in your hand, or wear it on an armband (preferably) or waistband.
- Open the Workout app on your Apple Watch, and choose Outdoor Walk or Outdoor Run.
- Choose your goal or select Open. Tap Start.
- Walk or run at your normal pace for about 20 minutes.
If you don't have time to finish the workout, you can complete 20 minutes over multiple outdoor Workout sessions. If you work out at different speeds, you should also calibrate for 20 minutes at each of the speeds you walk or run at. Whenever you walk or run outside using your iPhone and the Workout app, your Apple Watch continues to calibrate the accelerometer by learning your stride length at different speeds.
If you want to reset your calibration data, open the Watch app on your iPhone. Tap the My Watch tab, then tap Privacy > Motion & Fitness > Reset Calibration Data.
Update your personal information
Your personal information, such as your height, weight, gender, and age, is one of the things your Apple Watch uses to calculate how many calories you burn and more. To update your personal information:
- Open the Watch app on your iPhone.
- Tap the My Watch tab.
- Tap Health > Edit.
- Tap the item that you want to change and adjust it.
- Tap Done.
Learn more
Calibration can also improve the accuracy of your overall calorie estimations for other workouts in the Workout app, and the calorie, distance, Move, and Exercise estimations in the Activity app.