Which is more accurate, iwatch or chest strap heart rate monitor?

Hi

It is not possible to say which of a chest strap monitor or the built-in heart rate sensor on Apple Watch deliver more accurate results for you, specifically.

If you are concerned that your calorie estimations made by your Apple Watch (not iwatch) are inaccurate, then it may help to follow these steps:

If comparing calorie data recorded by different devices and their apps, then keep in mind that Apple Watch reports active energy / calories, whereas many other fitness devices and apps report total energy (resting + active calories).

When recording specific fitness activities, be sure to use the Workout app and to choose the activity type that most closely matches your workout:

• This enables your watch to use the most appropriate sensors and data sources when tracking results.
• If changing activity type during a workout session - as may be the case during Orange Theory workouts - use the option to add a new activity type to your workout without ending your session.
• Activity type choices also include HIIT.
• Choose Other for any workouts that are neither included within, nor sufficiently similar to, those in the list of main activity types (for which Apple Watch provides tailored calorie calculations).
• More information and instructions:
  • Work out with your Apple Watch - Apple Support

If you have not yet done so, update your iPhone and Apple Watch to the latest software, starting with your iPhone:

• Update the iOS on your iPhone, iPad, or iPod touch - Apple Support
• Update your Apple Watch - Apple Support

Check your personal information:

• Calorie estimations depend, in part, on your personal information.
• To check that this is accurate - and to update it over time:
  • On your iPhone, in the Watch app, go to: My Watch (tab) > Health > Edit - tap and adjust items, then tap on Done.

Check that you are wearing your Apple Watch correctly:

• For the best performance from the heart rate sensor - which is used continually during workouts, with readings used when estimating active calories burned - be sure to wear your Apple Watch snugly (but not too tightly) on the top of your wrist.
• Apple suggests tightening your Apple Watch band before workouts and loosening it again afterwards:
  • Wearing your Apple Watch - Apple Support
• For workouts that involve flexing your wrists, it may help to move your watch a little higher up your arm, away from the flexing joint.
• It may also help to check that the back of your Apple Watch is clean (along with your wrist, which I'm sure is the case):

• Cleaning your Apple Watch - Apple Support

If you experience issues with recording your heart rate during workouts, then, for more consistent readings, you may wish to consider pairing an external heart rate monitor / Bluetooth chest strap directly to your Apple Watch, in which case it will be used instead of the built-in sensor:

• Use Bluetooth accessories with your Apple Watch - Apple Support

Prior to calibrating your Apple Watch (see the next step), check your Location Services settings:

• On your iPhone, go to: Settings > Privacy > Location Services:
  • Check that Location Services (the main setting at the top) is turned on.
  • In the list of apps beneath, if Apple Watch Workout is listed (depending on your watch model), then set it to While Using.
  • Also enable options under System Services including Motion Calibration & Distance, Wi-Fi Networking and Mobile Network Search.

Calibrate your Apple Watch, resetting any existing calibration data and starting afresh:

• Calibrating your Apple Watch for improved Workout and Activity accuracy - Apple Support

Be sure to allow the arm on which you are wearing your Apple Watch to swing naturally during relevant workout activities and also during calibration.

If you remain concerned about calorie estimation inaccuracies, then I suggest that you contact Apple Support (remote diagnostics and/or mail-in service may be available, if required), make a Genius Bar reservation or visit an Apple Authorised Service Provider for assistance:

• US: Apple Watch Service Answer Center - Apple Support
• Elsewhere: Apple - Support