Power Consumption of Computer

If you try hard enough, you can probably find examples of 1000w or more....

I'll say under 200 watts. My four-core i7 tower with three hard drives normally takes about 120 watts, and a 19-inch LCD monitor should be under 75 watts.

The power rating will be found on a manufacturer's label attached to it, probably near the power inlet socket.

Ahhh--yup.

If you want real world, you will have to measure it. The mfr label, as suggested, is the lab value so engineers can plan accordingly for building and UPS loads, etc.

A general answer cannot be given because we don't know what type of power you are using, what power supply each PC/Mac uses, how many hard-drives, what type of motherboard, what the power usage scheme is, etc.

There is a lot of information which goes into this calculation, but simple measurement with the terminal running at some variance of maximum capacity would be a good start.