I'd recommend getting or borrowing a device call "Kill A Watt" . This plugs in to the wall, and in turn you plug in your device to it, and it will tell you how much power something is using. Truly an eye opener. I was not aware of just how much power many devices use even when "off". Anything with a clock, for example, will pull power - Stove, TV, Computer etc. These parasitic drains can add up significantly.
I have a couple of larger aquariums, and we were always worried about the power consumption. I did some research, and learned about DC pumps. Using the Kill A Watt, I could verify the reduction in electric consumption of over 50% by converting to DC pumps from AC.