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Anyone know how accurate the "eXtreme power supply calculator" is?


Jun 30, 2004
Others may differ, but I thought there was a prevailing opinion here at the forums that Extreme Outervision over-estimates power requirements.

upward-bias or no, I use it. Once you have a baseline that accommodates all your "stuff," you can add or subtract items to see how they impact the total.

It's an upper-limit guideline. You'll most likely never be taxing all the components in your system simultaneously even under full CPU load.

Here's my example. I built my machine last year to accommodate a hardware RAID controller, capture card, four drives, etc. I dialed in my over-clock settings. I tweaked all the nifty stuff, like "capacitor-aging." I came up with an estimate of around 610W, and chose a 650W (sustained) PSU.

Now -- when I run my OC settings to stress-test with PRIME95, my APC UPS monitoring software shows maybe 420W of power draw. And -- of course -- the disks aren't spinning like crazy, the DVDRW isn't burning, and the graphics card isn't occupied with Crysis.

For me -- I try to be energy-sensible, but I'd just as soon get a PSU that offers ample wattage than come up short. Also, some PSU's operate more efficiently in the upper-middle of their range.

I'd guess that they can determine within a fairly reasonable ballpark the wattage requirements for various over-clock settings, since those clock settings have a distribution of voltage and amperage requirements, so they'd base the computations on the average of a range of voltage settings. They would have to update their database of processors to keep up with newly released models and steppings, I would think.

Put it another way. Regardless of inaccuracies in one measurement or another, a decent but inaccurate "ball-park" estimate for each of several components broken down according to their power needs should come up with a reasonable estimate for the whole. The more specific they make the inputs to the calculator, the more likely that their "upper-limit" is ample to cover your bases.


Aug 25, 2001
Interesting, for an E2140 @ 3.2Ghz, 1.425v (BIOS), Radeon X1950Pro PCI-E, 1 320GB WD SATA HD, 1 IDE DVD burner, it gave me an estimate of 365W.

I have a ThermalTake 430W (yes, I know, I know. But it was cheap) powering it. Seems to run fine for me.

I have it plugged into a 330W/550VA UPS.

Ok, this PSU calculator is utterly wack.

In the "overclock your CPU section", I put in my E2140, and OCed it to 3200Mhz @ 1.42v (couldn't enter 1.425). It shows my CPU as taking 164W.

Now, to check my new builds, I put in a Q6600 G0, and OCed it to 3600Mhz @ 1.45v. It shows the CPU taking only 192W!

How can a lower clocked, lower volted, dual-core CPU take nearly the same amount of power as a higher-clocked, higher-volted quad-core?

Either the quad should be taking around 300W, or the dual-core should be taking closer to only 100W.

Overall, it shows my Q6600 @ 3.6Ghz, 1.45v, with crossfired HD4850s, some fans, 5 SATA HDs, DVD, no floppy, taking 670W. Yet, in this thread , someone replied to my query about the Antec EarthWatts 650W, saying that it would be enough.


Jun 30, 2004
Oh, I'll agree that it's "inaccurate." But the bias is in favor of a PSU with more than enough sustainable wattage.

Larry's friend is probably right -- he'd never need more than the 650W Antec. But like I said, quantitative assessment aside, many PSU operate more efficiently in the upper-mid-range of their full sustainable capacity. Between the two, he's probably still drawing much less juice than the Antec's capacity.


Diamond Member
Jul 23, 2005
Haven't tried it for a while. It says my current system requires...397W.

- 143W for the GPU
- 105W for the CPU
- 68W for the HDDs and ODDs
- 32W for the 7x120mm fans
- 25W for the TV tuner and sound card combined
- 9W for the RAM
- 15W for misc things


Diamond Member
Apr 19, 2005
It shows my E21xx@3, 1HD, single 6200LE, 3x120mm, 4GB RAM = 360W. I think it's way overestimated. My reading from the wall shows about 150W and under when system loaded with HD spinning and everything working hard. Their estimate is way too high but definitely safe if you follow it.


Feb 11, 2006
That thing is garbage. It says my system (below) should use 275W (at 85% load) but I've tested it myself with a P3 Kill-a-Watt meter and it uses about 110W idle and 180-190W under 100% load.

edit: Ok I suppose "garbage" is a little harsh. If you follow their guidelines (remember they sell PSUs) you'll be ok though you'll be buying way more PSU than you really need.

That said, I have a 500W PSU for my system that uses less than 200W... :)

Remember too it's not about total wattage but what it's got on the 12v rail(s). On a modern 12V ATX system your CPU, GPU(s) and hard drives all run off the 12v rail. If your PSU only has 13 amps on a single 12v rail (13a x 12v = 156 watts) that's not going to be enough if your cpu needs 110w and your gpu needs 105w...