The USBC-VAMETER will display voltage, amperage, and the calculated wattage on screen. If you would like to manually calculate the wattage (how much power a device using) you can follow this simple formula: 

The power (P) in watts (W) is equal to the voltage V in volts (V) times the current (I) in amps (A), P = V × I.

Example: A device is charging at 20V, 5A: 20V × 5A = 100W.