I was having a bit of a debate with a friend about how much electricity a computer uses. It began when he said it sometimes took 12 hours to download a movie, and I said, for the price of electricity it would be cheaper to rent the movie for basically a dollar at the nearest rental store. He disagreed. Finally after realizing that his total monthly electric bill was around 50 dollars (here in Japan) I realized he may be right.

What is the straight dope on this. Do computers suck the juice?

Not so much. Typical computer power supply is rated at around 300 watts or so. If we’re generous and say this is how much power the computer draws all the time (it’s not), and add, say, another 100 watts for the monitor (again, being very generous), that’s a total draw of 400 watts. Total energy used during 12 hours would, therefore, be 4800 watt-hours or 4.8 kilowatt hours. National average for electricity in the US is around 8-9 cents or so per kWh. Let’s say 10 to keep the numbers round. 4.8 x 10 is 48 cents. Seems pretty cheap for a movie to me, and remember that this is a worst-case scenario. In actual practice, computers typically draw much less than the rated power of the power supply–100 to 150 watts is more typical during normal use. And monitors draw even less–around 60-70 watts for a CRT and 20-30 for an LCD.