You can easily measure how much electricity your AC uses per hour by looking at the spinning disk on your electric meter.
First you need to find the Kh factor on your meter. Here's an example circled in yellow. Mine says 7.2.
Now measure how fast the meter disk is spinning when your AC is not running.
I timed mine at 39 seconds per revolution.
The formula to calculate the amount of electricity being used is 3.6 x Kh_factor / seconds_per_revolution.
So it's 3.6 x 7.2 / 39 = 0.66 KWH without the AC running.
Now time the meter disk with the AC running.
I timed mine to be make 3 complete revolutions in 20 seconds. So it's taking 6.7 seconds per revolution.
That's 3.6 x 7.2 / 6.7 = 3.87 KWH with the AC running.
So the AC is using 3.87 - 0.66 = 3.21 KWH which is pretty good for a 13.5 SEER 4-ton system.
Of course you have to make sure no other electric appliance is going on/off between the two measurements.
I'd like to hear what kind electric usage other people are seeing with their systems.