(Odograph - n. an instrument recording distance traveled, especially by a pedestrian.)
I have a Kill-A-Watt monitor that I like way too much. It was a lot of fun for forty dollars or whatever. That device is intended to sit on the electric cord and total up the usage over time. That is the best way to use it, measuring (for instance) a week's worth of TV.
Alternatively we can use the monitor to grab an instant reading, just plug it in and watch the watts being drawn. That is much less reliable than monitering over time (even for things like TVs that are fairly steady-state, but especially for things like refrigerators or computers that vary over time).
This calculator extends the instant reading to month and year usage, and works out the cost for that energy.
please enter some values and press "(re)calculate"