As has been said, using the in-car equipment or Carwings will not yield your actual electricity use. You will need to account for losses in the charging system and batteries. As has been suggested, you could get some add-on equipment to meter your use, which understandably you don't want to spend money on.
But there are 1 or 2 other simple (and free) methods:
1) Your EVSE may have a meter built into it. See if that's the case first. If so, you're all set! Even my Aerovironment EVSE has metering capability and I can log onto their web site and see exactly how much power it is using from the wall. Granted, it may be a special unit because I'm in a pilot program through my utility so they needed extra monitoring equipment.
2) The other method is to just assume a loss factor. Once you go through the math (or check on Carwings) to determine how much kWh the car thinks it used, you would then divide by that loss factor to determine how much you used from the wall. The usual loss factor for L2 charging quoted is 85%, so for example if you determined you used 18.0 kWh, you would divide by 0.85 and get 21.2 kWh from the wall.
I recently did a fairly controlled experiment to determine my own factor, and while the accuracy available from the car/Carwings is pretty low, it does give a reasonably good figure. Here is my data:
Miles driven: 117.5
Car efficiency meter reading: 4.4 mi/kWh
Consumed power from the car's info: (117.5 / 4.4 = 27 kWh; actually considering it could have been anywhere from 4.35 to 4.45 mi/kWh, the range is actually 26.4 to 27.0 kWh)
Actual power usage from the EVSE (two charging events): (13.83 kWh + 18.77 kWh = 32.6 kWh)
Loss factor = 27 kWh / 32.6 kWh = 83% (calculating the range, it's between 81.0% and 82.9%)
One of the two charging events was a 100% charge, so it's going to be less efficient due to the taper-off in charging, while the battery fan still runs, causing overall less efficiency. But since I sometimes charge to 100%, I think it's fair to include that as part of my measurement. This would account for the fact that my loss factor is less than the 85% usually quoted.