So... how DO you calculate the Power Supply required?

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ballistic90

2[H]4U
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Nov 17, 2010
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Is there a method to calculate how large of a power supply you need? Is as simple as something like this: Power Draw = (Power rating of motherboard + power draw of the video card + ram power requirement + drive power draw), or are there other considerations? I've never had to really look deep into getting power supplies before.
 
I just hook up my Kill-a-watt and make sure that my consumption isn't more than 120% of my PSU's rated output.

I measured this on my 1000w PSU so I figure I'm good to go.
 
KAW's aren't very accurate. I've seen them swing in nearly 100w in either direction with the same load.

I take the max draw of the video cards, max draw of the cpu, add 10w per HDD/ODD/SSD, add 50-75w for mobo/fans, then multiply by 1.1 to give myself 10% overhead. Then buy a solid PSU that is either at or above that value.
 
As Jorona said, KAW's are not accurate with Active PFC PSU's. If you really want to test a PSU's power draw you're gonna need to spend at least $150 on a good unit.

What I do when figuring out how much power a build needs is by reading good reviews on the parts needed for the build. Specifically the CPU and GPU power requirements as those are going to be the big players. Once you get that calculated, figuring out HDDs, fans and other peripherals are easy.

What is your system build? Be specific with parts, especially the PSU you intend to use.
 
Jorona said:
KAW's aren't very accurate. I've seen them swing in nearly 100w in either direction with the same load.

I take the max draw of the video cards, max draw of the cpu, add 10w per HDD/ODD/SSD, add 50-75w for mobo/fans, then multiply by 1.1 to give myself 10% overhead. Then buy a solid PSU that is either at or above that value.
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For me, I have at least a 130 to 200w leeway, so I should be fine.
 
ballistic90 said:
Well, it turns out that the PSU I have is more than enough for what I was planning. Huh.
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Well you also have to determine if it's of high enough quality for what you're planning as well. I've seen too many people stick with crappy 500W to 600W PSUs just because some PSU calc tell them it's enough power.
 
Dangman said:
Well you also have to determine if it's of high enough quality for what you're planning as well. I've seen too many people stick with crappy 500W to 600W PSUs just because some PSU calc tell them it's enough power.
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I bought it some time ago, but I spent a little extra to get a brand name power supply, and according to every calculation I've done, I have somewhere between 120 W to 200 W more than technically neccesary on the PSU.
 
Your posts are so vague it's rather aggravating and annoying.

What does the calculator say your power requirements are?
What exact PSU do you have?
What are your system (planned or current) specification?
 
ballistic90 said:
I bought it some time ago, but I spent a little extra to get a brand name power supply, and according to every calculation I've done, I have somewhere between 120 W to 200 W more than technically neccesary on the PSU.
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Yes but not all brand name PSUs are actually good. So please answer SKillz's questions.
 
That calculator say my system draws 575w and I should have a 625. Looks like it is time for more power!!
 
Also remember that the efficiency of your PSU drops after time/use, so get some extra quality power just for that regard.
 
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