I charged an iPad Pro (12.9 Inch) and measured the power consumption (at 120V and 230V). According to the specs, this iPad has a battery with a capacity of 40.88 Wh.

Procedure: when the iPad Pro turns itself of because of a low battery, I started to charge the iPad with an Apple A2347 USB C charger and measured the AC power consumption of this charger. It consumes around 21 Watt, this value starts to diminish when the battery approaches full charge. When at 100%, the charger will still deliver power, slowly decreasing to 3 Watts, and then it stops delivering power for charging. At that point, I stop the power consumption measurement.

I did not use the iPad while charging.

This measurement was done twice: at 120V 60Hz and 230V 50Hz (using an AC power supply).

There’s not much difference between the two measurements, but what I’ll certainly take away from this test, is that it takes around 57 Wh of AC power to charge a 40.88 Wh battery!