If you've recorded a session with your Apple Watch, we use Apple's Active Calorie count that the watch calculates. If you didn't use the Apple Watch to record the session, we use the following information to estimate calorie burn:
- Biological sex, if you've entered it into Apple Health and given us permission to access it
- Workout distance
- Workout duration
The math is a little fuzzy, since calculating calories is difficult, and the verdict is still out on how to do it exactly.