Can you really find out how much it uses? Yes but it would require you put a meter on it to figure out exactly how much it uses. You can just do the math for it but the numbers you come up with will be wrong.....
#1 Doing the math will not figure in the down time of the unit. The AC unit is always on and the fan is always running. However the parts that draw the most power cycle on and off. They will turn off when the correct temperature is reached or to give itself a break.
#2 You need a wattage or amperage number to do the math. The number printed on the unit is not a real world number. The unit my say 12amps but that is normally surge amps and once the unit is settled it will consume less.... say around 8 amps.
#3 Getting the correct numbers are based around knowing what voltage you are using. A normal US house will see voltage in the 110-125 range.... you need to know what your is to find the exact number.
Doing the math is simple, but the results will be higher than they really are. You could however come up with a rough number.
Follow the link below to get the equations.
You could try this, never used it so I dunno how good it is.
Really the easy way would be to compare a bill from last year when you didnt have an air conditioner.
If you have a 12 amp AC unit it uses roughly the same as 12 100 watt light bulbs. About the same as a Microwave oven when its running. About half of what a hair dryer uses. 15-20 Times what a TV uses.............