# How much power does my computer use?

I’m trying to calculate how many kilowatt/hours my computers use in a month. I have with with a 250watt power supply, which is on basicly 24/7 . I have a second which is on about half that time, whos power supply is 300watts. I have 2 monitors, I’m not sure what the draw is. How would I calculate how much power they use per month?

The 250 watts figure is the rated power. Actual power consumption is likely to be only a fraction of the rated power (but I don’t know how much exactly).

Assuming the computer actually draws 250 watts (¼ kilowatt), it will use ¼ kilowatts * 24 hours /day * 30 days / month = 180 kilowatt-hours per month.

The monitors are easy. Take the amp rating off the back and multiply by 115Hz to get watts. The rest is the problem of course, since it varies by how many boards are installed, and some draw little power when not in use. Add in the printer, scanner, fax, speakers and camera only when in use.

For a crude estimate-
Pacific Gas & Electric just sent us all brouchures listing a “computer with color monitor and laser printer: \$1/day”.
No indication of how long it’s left on etc.

Actually, not that simple. The amp rating is the maximum that the monitor will draw, and that usually happens when turning it on, when the circuitry and CRT are powered up and the degaussing circuit is activated. Actual usage is a bit less. Plus, most monitors are power-saving these days (you do have your power-saving features turned on, right? Or at least turn the monitor off when you’re not using it, which will also prolong its life).

Also, typically you’d use 120 volts (not Hz), multiplying it by the current, to give a rough estimate. For an accurate answer, you’d need to use an ammeter. The monitor’s manual may give typical usage, though.

Most ammeters you find are not going to be sensitive enough to give you good readings on a monitor. The manufacturers don’t publish much on their unit’s power use because it varies greatly in different applications. Use the auto power-down instead of a screen-saver, and even go further and shut it off all they way when you go home for the night, or weekend, or what ever.

Older laser printers and photocopies really suck the juice. If you have one that doesn’t have an auto-sleep mode then you can save yourself a fortune by shutting it off anytime you aren’t going to use it for a while.

If you would read the manual, in the back it states how much it uses. Check the power saving mode, it uses like 35 watts for the monitor & computer combined. spiffy.