How to determine needed PSU wattage

[Me1z]

I can tell you guys are getting tired of answering and re answering the same question. So rather than posting multiple potential rig scenarios and wasting your time, I would like to know how to figure it out for myself. How do you 'calculate' needed PSU wattage? Is there a simple equation? Do you just add up each components watts?

[FloRolf]

experience.

[Jamdude]

If you're putting the parts together in PCPartPicker then it'll tell you, if not then use something like this.

[_ASSASSIN_]

experience.

wow thanks

 

there are PSU wattage calculators have them, BeQuiet, Newegg, and many other companies have one.

[miyabwah]

I always use this formula to calculate my PSU:

 

[(cpuTdp + gpuTdp) * 2 ] + [(numberOfGpus -1) * gpuTdp]

 

Works every time.

[Shrubpig]

You can just add up the wattage of each component. After awhile though, you can just sort of guess. Usually it's around 550W

[TymmVonD]

Build your rig in PCpartspicker and look at top right. It displays est wattage. Or use a number of PSU calculators.

[Wheelzz]

Those PSU wattage calculators seem to work fairly well.

[WoodenMarker]

Combination of experience, what you see works for other people, benchmarks, reviews, some specs, kill-a-watt measurements, and/or psu calculators. (I tend to avoid psu calculators since they are highly inaccurate for the most part).

[s3ns3]

well a decent 550W psu is more than enough for high end cpu+ high end gpu+lots of drives and fans . so start from there

 

so from experience couse psu calculators are trash im my opinion

[orangecat]

I just guess. 500 watt should be good for any mid range gaming system but for a high end I would go 650+. I have a 3570K @ 4.4 and a GTX 460 and I'm running a 700 watt PSu and its pretty overkill my system maybe uses 300 watts.

[Me1z]

experience.

 

You can just add up the wattage of each component. After awhile though, you can just sort of guess. Usually it's around 550W

 

Yes, I realize you can guess using past experience. I have built multiple computers before. The issue is once you get into the realm of unconventional computers or cutting things as close as possible.

 

Build your rig in PCpartspicker and look at top right. It displays est wattage. Or use a number of PSU calculators.

 

Those PSU wattage calculators seem to work fairly well.

 

Like I said before, the issue is when you get into the realm of unconventional computers. Extreme Outer Vision has the most options of any calculator I've seen, yet even they require you to pay them if you want to calculate say, 6 gpus.

[Me1z]

 

I always use this formula to calculate my PSU:

 

[(cpuTdp + gpuTdp) * 2 ] + [(numberOfGpus -1) * gpuTdp]

 

Works every time.

 

 

Thank you, Lanoi 

[The Syndicate]

PCPartpicker will tell you.

[Wheelzz]

I don't know exactly how to get an accurate representation manually. I'd say try to find the TDP of GPUs, CPU etc and add everything up. Case fans only use a few watts, HDD probably use about 20W for a typical 7200RPM drive (some higher and many lower) and an SSD would use even less. I am not sure about a mobo, I hear around 50+ Watts for a decent board.

 

GPU power usage can be hard to come across. The Asus site says that the GTX 770 DC2-OC uses up to 300w, but Techpowerup's Review shows that the card only uses just over 210 watts even during stress testing, and less than 200w during gaming. I believe most of the other reviews show similar results as well.

Edited February 2, 2014 by Wheelzz

[Wyre]

http://www.extreme.outervision.com/psucalculatorlite.jsp

 

I have found this to be a very valuable tool. Just plug in what you have or what you are ordering and voila it will calculate the power requirement, and recommended power for the parts selected.

[Wheelzz]

 

I always use this formula to calculate my PSU:

 

[(cpuTdp + gpuTdp) * 2 ] + [(numberOfGpus -1) * gpuTdp]

 

Works every time.

 

This is not taking into account motherboard, drives, and any other device's power usage.

[Me1z]

This is not taking into account motherboard, drives, and any other device's power usage.

 

I saw that, but it does over estimate by adding the equivalent of a second CPU and GPU at full usage which would probably be more than the motherboard, ram, drives, and fans combined.

[MG2R]

This is not taking into account motherboard, drives, and any other device's power usage.

By taking your CPU+GPU and multiplying that by two, you factor in a beast overclock on both + extra headroom for stuff like your mobo/couple HDDs/RAM

[Faa]

The bios is handy to find out what your gpu will pull max.

#1 http://www.techpowerup.com/vgabios/128444/asus-gtx670-2048-120911.html

At stock settings so 100 power target or in percentage 100% TDP* it will pull 157W, be aware even at 99% load the card might not sit at 100% tdp but something like 80-90% - at this point if you increase the power target it won't pull more power. Lets say it sits at 120% TDP then it pulls 180W.

Some minor things that can be helpful:

- 6pin -> 75W
- 8pin -> 150W
- pcie socket -> 75W

So a 6pin+8pin card could be fed with 300W of power you can exceed this with a bios mod but the stock bios would always be lower than that 300W eg gtx 780 dc2oc. A 690 (6+8pin) is locked to 170w - a classified (8+8pin) is locked to 330W.

#2 With cpu's you can't get accurate results we don't have monitoring tools like the power target on GPU's and monitoring tools like Coretemp or HWinfo aren't accurate at all. First thing you should be understanding is the TDP. A 3930K has a TDP of 130W but the max power draw is much higher than the TDP value. TDP is just a cooling spec a requirement of x amount of heat dissipation under normal conditions like real world apps, many people are using the term wrong. If you need proof for this: http://www.intel.com/content/dam/doc/white-paper/resources-xeon-measuring-processor-power-paper.pdf @ page 2

Usually what I do is, looking for graphs where the cpu power only has been measured - there are plenty @ OCN. If you know the cpu is pulling x watt @ 100% and if your game never exceeds 50% well divide it by 2 gives you almost an accurate idea of how much it needs. Be aware prime95 100% cpu load pulls much more power from the wall than a stupid rendering prog pushing your cpu to 100%.

#3 Chose a certain wattage for your own daily normal usage not for the worst case scenario unless you're mining or folding 24/7. Giving an example: With a 3930K+OC & 2x 780's OC running them at their max like prime95+furmark should easily run on a 1000W psu but if I add a 3rd 780 it won't happen but in a game like BF4 it will work perfectly. 
 

[Wheelzz]

Some minor things that can be helpful:

- 6pin -> 75W

- 8pin -> 150W

- pcie socket -> 75W

So a 6pin+8pin card could be fed with 300W of power you can exceed this with a bios mod but the stock bios would always be lower than that 300W eg gtx 780 dc2oc. A 690 (6+8pin) is locked to 170w - a classified (8+8pin) is locked to 330W.

Are you saying a GTX 690 only uses 170w at load? As far as I've seen, a typical 770 will use around 200w at load.

 

Also, I take it the power is only being drawn from the PCI-E slots if you actually have them populated? 

 

A card doesn't always draw all the power the PCI-E connector setup allows for right? IE a 6+8pin card using only about 200w.

[Faa]

Are you saying a GTX 690 only uses 170w at load? As far as I've seen, a typical 770 will use around 200w at load.

Yes. 770's arent really optimized like the 690. Just see here the difference between a single 690 and 2 690's

I've done earlier testing when I had the ax860i to see if the power values from the bios are accurate and suprisingly they were. Corsair link allows you to monitor the amps from a pci express cable even. Temperatures are a nice indicator as well, a 400W GPU can hardly be cooled @ air even if you can it's going to be noisy something the 690 isn't.

[Wheelzz]

Yes. 770's arent really optimized like the 690. Just see here the difference between a single 690 and 2 690's

I thought you were saying a GTX 690 uses 170W during gaming load, there's no way that would be true.

[Faa]

I thought you were saying a GTX 690 uses 170W during gaming load, there's no way that would be true.

It does. http://www.techpowerup.com/vgabios/127271/zotac-gtx690-2048-120421.html

[MG2R]

A card doesn't always draw all the power the PCI-E connector setup allows for right? IE a 6+8pin card using only about 200w.

Electronic circuits only draw as much power as they "need". What they need is defined by Ohm's law: I = U/R

(I=current, U  = voltage, R = resistance)