How many watts do I need? (Varied Calculators Give Me Extremely Different Estimates)

krunchykarrot · Oct 5, 2014

Intended build, have the money but want to buy everything together. Not sure what wattage power supply to get:
Nzxt s340 - Black
Intel i7-4790k
ASUS Maximus VII Hero
Kingston HyperX FURY 16GB (2x 8GB) DDR3 1600MHz Black
SanDisk Ultra II 120gb ssd
2tb barracuda 7200rpm
2 x msi R9 270x
CM Seidon 120V CPU Cooler

First build ever. Pretty Excited.
Any feedback, any changes?
What is the appropriate wattage?

Agera One · Oct 5, 2014

Recommended to refer these links before buying PSU:
Power Supply Units Tier List
Power Supply requirements of various GPUs

Warfyr · Oct 5, 2014

I am by no means the know it all of psu information here on the forums and one of those will probably stop in and answer this.. but at a minimum I would personally go no lower than 850 80 bronze.. if your estimates told you higher than that go with those numbers.

in response to agera.. he has 2X r9 270s hence my guess at 850.. assumed oc as well

Agera One · Oct 5, 2014

OOPS!! I din't notice the "2x" 700 W is enough for crossfired R9 270x system. 800 W or more for overclock/ future proof. Make sure you have the necessary connectors pins for the MSI version 270xs.

InvalidError · Oct 5, 2014

If you are building new, you might want to consider 1x R9-290/290X instead of 2x R9-270X: about the same price, performance lower power and without the potential performance quirks or game compatibility issues that often come with SLI/CrossFire.

If you tack on a 50% margin on top of your absolute minimum power requirement to keep your PSU below 70% at full load, you need a ~650W PSU either way.

Warfyr · Oct 5, 2014

700w appears to be your answer according to these 2 fine knowers of things above me. That puts you slightly above optimal in case you wanna oc or w/e

Agera One · Oct 5, 2014

InvalidError :

I never played on a multi-GPU system. It has game compatibility issues?
Also Can you explain the last sentence you said about PSU. I don't understand clearly.

Warfyr · Oct 5, 2014

I have read that psu's are optimal at 50% load.. this is what he is referencing (i think) he is stating what it would take to keep full load under 70% IE the 80 bronze is rated to 80% so under 70 is still optimal even if its not bronze 80 rated..

I think i got that right.

InvalidError · Oct 5, 2014

Agera One :

Games and drivers often require patches to work correctly with SLI and Crossfire. If you are going to spend $350-400 on GPUs, getting a R9-290/290X would be a safer bet than 2x R9-270X... and you get 4GB VRAM as a single memory pool instead of two GPUs with only 2GB each.

As for the 70% thing, that is because running PSUs at close to 100% is usually not good for long-term stability and PSUs are usually most efficient in the 40-70% range. With either setup, I would expect your typical PSU output while gaming to be around 350W with peaks possibly up to 400W. Add 50% and you get 600W. I am not aware of any popular PSU models at 600W but there are quite a few around 650W.

DonkeyOatie · Oct 5, 2014

The 80% in a power supply's rating is its efficiency. An 80% 640 watt supply puts OUT 640 watts, but draws IN 800 watts from the wall. 800 x 80% = 640.

InvalidError · Oct 5, 2014

DonkeyOatie :

The efficiency rating (whatever flavor of 80+ or none at all) and the recommended maximum load (about 70% on good PSUs) on a PSU are two separate things.

DonkeyOatie · Oct 5, 2014

That is completely true. I was responding to an earlier confusing statement (and I should have done a better job of it)

Running a power supply at around 50% of its rating most of the time is a very good thing.

Warfyr · Oct 5, 2014

ya... what yall said is what i meant but i guess i worded mine funky as well.. I was attempting to say that it could run enough under 70% inso that it would not need to make it to 80%(maximum load). Hence it would not matter if it was 80 bronze or not since it never needed to get to 80% any way. I should have separated the 2 thoughts about the 50% being optimal and the fact that it only needed to ever run to 70% in my wording i guess lol.

I was however unaware that the 80s had a recommended run of 70% but again you want to be closer to 50-60 any way for life longevity and so on.

I feel like i just did it again... lol w/e the question has been answered go with those smart people's answers

to summarize here.. a 650-700w would always be in a some what optimal percentage so long as you didnt add another card or w/e. at 700 you could over clock a little more and it you want to future proof it go 800+

Dark Lord of Tech · Oct 5, 2014

PCPartPicker part list / Price breakdown by merchant

Power Supply: EVGA 750W 80+ Bronze Certified Semi-Modular ATX Power Supply ($79.99 @ Micro Center)
Total: $79.99
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2014-10-05 16:55 EDT-0400

InvalidError · Oct 5, 2014

Warfyr :

This is still worded weird as heck since it still sounds like you are confusing 80% efficiency with 80% load.

Even if you are loading the PSU only to 10-20%, 80+ basic/Bronze/Silver/Gold/Platinum/Titanium efficiency still matters to people who want maximum efficiency across the whole range from idle to whatever their system's peak power draw is.

DonkeyOatie · Oct 5, 2014

And not everyone's power is couple of $ a month cheap for a computer.

tiny voices · Oct 5, 2014

750w is the short, correct answer.

Get the unit SR-71 linked.

Warfyr · Oct 6, 2014

InvalidError :

Yep.. I agree that is how my wording makes it look. I defer to your better explanations and judgement on this one because my intent it there but my words are broken.. if i see this question again ill come back here and copy paste your explanation lol.

Agera One · Oct 6, 2014

InvalidError :

Agera One :

Games and drivers often require patches to work correctly with SLI and Crossfire. If you are going to spend $350-400 on GPUs, getting a R9-290/290X would be a safer bet than 2x R9-270X... and you get 4GB VRAM as a single memory pool instead of two GPUs with only 2GB each.

As for the 70% thing, that is because running PSUs at close to 100% is usually not good for long-term stability and PSUs are usually most efficient in the 40-70% range. With either setup, I would expect your typical PSU output while gaming to be around 350W with peaks possibly up to 400W. Add 50% and you get 600W. I am not aware of any popular PSU models at 600W but there are quite a few around 650W.

Thanks !

krunchykarrot · Oct 8, 2014

Thanks everyone for the responses. Been really helpful. I took your advice and have shifted up to a 290.

How many watts do I need? (Varied Calculators Give Me Extremely Different Estimates)

Reputable

Splendid

Reputable

Splendid

Titan

Reputable

Splendid

Reputable

Titan

Champion

Titan

Champion

Reputable

Retired Moderator

Titan

Champion

Titan

Reputable

Splendid

Reputable

Share this page