Keep your data accurate

Apple Watch uses the information you provide about your height, weight, gender, and age to calculate how many calories you burn, how far you travel, and other data. In addition, the more you run with the Workout app , the more Apple Watch learns your fitness level—and the more accurately it can estimate the calories you’ve burned during aerobic activity.

Your iPhone GPS allows Apple Watch to achieve even more distance accuracy. For example, if you carry iPhone while using the Workout app on a run, Apple Watch uses the iPhone GPS to calibrate your stride. Then later, if you’re not carrying iPhone, or if you’re working out where GPS is unavailable (for example, indoors), Apple Watch uses the stored information about your stride to measure distance.