An easy, after the fact method, can be done if you have a digital meter readout of use. If you have ever read your meter, sort of daily, at the same time you can get a fairly good idea of your useage, KWH divided by days. Our bills show a daily useage for the last year already computed, which runs 1.1 to 1.5 KWH depending upon the season. You should see a daily increase in the readings if you plug in one of those window units for a few days. If you have feel for your daily use and plan on doing some canning or something similar on an electric stove............you'll be amazed what that can do to your bill. Did just that a few years back when we did some dill pickles. Our juice costs about 11 cents/KWH at the end of the bill (including all the BS charges)