How to: Find out the actual power usage of my computer?

I have heard this question asked quite a few times in threads....."Is there a way to calculate how much power my PC is consuming?" or "Has this power supply got enough wattage for my setup?". Until recently I thought the only way to answer the above question was to guess the power usage of your system using the separate power requirments of the components. However, this method is unreliable as it depends on:
a) the usage of the component (i.e. load or idle)
b) the state the component is in (power requirements alter as the component ages)

There is a way to continuosly measure the power usage of your system...and that is with a plug-in mains power meter. They fit into the wall socket and allow you to measure the power/voltage/current being drawn from your PC. They also work out the cost of running your PC in KWH. You enter the cost per KWH and it will calculate how much your computer is costing to run. This could be useful for people with folding farms....who want to calculate how much extra it would cost to for example add another computer.

Here is a link to show how they operate:

http://www.the-gadgeteer.com/review/...monitor_review

Another thing which must be taken into account with PSU's is the efficiency rating of the PSU. Take my Tagan U22 480W PSU for example...it has a 77% efficiency rating at full load. This means that at full load for every 100W supplied to the PSU only 77W are converted into useful power output. This must be taken into account with the power meter reading. Here is an example for my 77% efficient PSU; if the power meter reading is 300W, the PSU will actually require 300/0.77 = 390W of input power to produce the 300W of output power. Consequently, the efficiency factor is absolutely vital when calculating if your PSU is able to produce enough output power to supply your system.

Your PSU's efficiency rating should be written on the side of your PSU, but if it is not, then just google the name of your PSU and you will almost certainly find it there.

They cost around $30, and could be really important for those with an SLI/crossfire setup who want to know if there 400W will cut it.

If anyone wants me to try and find a link to where to buy one then please dont hesitate to ask.

Thanks Burn...you are right I forgot about the efficiency of the CPU. This isnt anything major though as almost all PSU's have their efficiency ratings written on them. I will add this to the FAQ, thanks

This isn't the place for that type of question. You should start a new thread using proper English....alternatively you could do what the FAQ says and buy a power meter to find out if you PSU is undersupplying.

No I dont think it is telling porkies....computers just generally dont require as much power as people think they do! I am glad you tried it out....hopefully this has helped prove that in most cases a 600W PSU is overkill.