How does the Apple Watch track calorie burn
How does the Apple Watch track calories
Question marked as
Top-ranking reply
It uses algorithms, based on scientific data, related to heartrate and activities. Is it 100% accurate? Not really, as no two human bodies burn calories in the same exact way. But it's a good guide and you can calibrate some things on your watch to help it be more accurate.
Read this --> Get the most accurate measurements using your Apple Watch - Apple Support