Metabolic Equivalent values or METs are used to ensure your calories represent how you swim, METs are a measure of energy expenditure per kilogram of bodyweight per hour and are specific to the activity you are undertaking. A list of example MET values for a range of activities can be found at the link below:
The Compendium of Physical Activities Tracking Guide (pdf)
Using data collected from your swimming history and the stroke type and pace of your length we calculate a MET range, from an easy swim to a hard swim. Our algorithm will then estimate the difficulty of that length and therefore what MET value that equates to. Calories are then calculated using your bodyweight, the time of your length, and the MET value in the following equation:
Cal = MET x Bodyweight (kg) x Time (hours)