September 4, 2015

You Probably Don’t Need As Much Power As You Think!


One of the most common questions I am asked by readers is for recommendations on the best power supply for their mini-ITX gaming systems. It’s one of the more popular topics on our forums. Not surprisingly, many builders are faced with dilemma of trying to spec a power supply that will suit their builds. It needs to have enough power to run high end components, yet be compact enough to fit into their chosen mini-ITX case; two requirements that do not often go hand in hand.

There is a solution, but it requires that I go out on a limb and suggest something that I have recently learned with my mini-ITX builds and from some research into full size gaming rigs. No doubt, it’s something that many people (including a few manufacturers) might disagree with:

You don’t need as much power as you think you do!

Most system builders have no concept as to how much power their computer actually uses. I know I didn’t. When I laid out my first ITX gaming system, I figured that I would need a rather large power supply given that my chosen video card, a Gigabyte Radeon HD 6850, carried a minimum power supply rating of 550 watts. Wanting to leave myself a little overhead, I built my system with a 700w OCZ power supply.

Being a standard ATX PS/2 unit, the OCZ power supply required the use of a mini-ITX chassis that would support it. Fortunately, the Lian Li PC-Q08 turned out to be an excellent case for my build. It turned out to be a powerful and compact gaming system.

However, my quest had always been to make my systems as small as possible and although the PC-Q08 is a mini-ITX case, it’s one of the larger ones available, partly due to the ATX PSU support. Many smaller mini-ITX cases won’t support an ATX unit.

So what about a smaller PSU?

There are several choices of power supplies that are smaller than the ATX, but smaller form factors also mean smaller capacities.

SFX power supplies (sometimes referred to as micro ATX PSU’s) offer a possible alternative to a full size PSU. A quick search on Google shows that several reputable manufacturers make SFX power supplies up to about 400 watts. Not only will these SFX power supplies allow the use of smaller cases, but thanks to the often included adapter plates, they can also take the place of larger ATX power supplies to free up space inside the case.

Too bad 400w isn’t enough for a gaming system.

Or so I used to think. As it turns out, 400 watts is more than enough power to run a high end mini-ITX gaming system (and probably most ATX systems too). I understand if you don’t believe it. I didn’t. Not until I plugged my system into a power meter and saw how much energy it actually uses.

The chart below shows the maximum number of watts that the system pulled during each task:

The system in question consisted of:

  • Intel DH67CH Motherboard
  • Intel i5-2500K Processor
  • Gigabyte Radeon HD 6850
  • 2 x 2GB G.Skill Ripjaw Gaming Series DDR3-1333
  • Western Digital 500GB Caviar Blue HDD
  • Samsung DVD-RW
  • Intel Stock Cooler
  • OCZ 700w ModXStream PSU
  • Lian Li PC-Q08 Chassis

I tried several different combinations of applications and benchmarks on different settings and 213w was the maximum draw I could get. Taking into account the 86% efficiency rate of the OCZ ModXStream series, the components inside my PC are peaking at 183w.

Even allowing for extra overhead, a quality 80+ certified SFX power supply around 400w would be sufficient for my needs. Several manufacturers offer such a model. Silverstone offers the ST45SF, a 450w SFX unit and Ultra has a 400w X4 modular SFX unit that will also cut down on cable clutter.

Next time you’re taking on a mini-ITX build, don’t be discouraged by small chassis with SFX power supplies. Take a few minutes to figure out just how much power your system actually needs and chances are that compact SFX power supply will be up to the job.


  1. Greg says:

    I have a mini-itx rig that includes an E8400, Radeon 5570, 4GB memory, 320GB HD and I run it all off a 150W pico psu. Now my monitor is only 1280×1024 but I bet quite a few people still have those. I can't game on super high detail, but for the casual gamer that I am, it works just great! All settings are on medium to high with little to no jumping. You really don't need 185fps, 30 or so will do just fine.

  2. eXces says:

    Thx for the tips!

  3. Alister says:

    Thanks so much for posting this!
    I was bummed that when building my new computer I'd need a huge 700w+ psu, but it appears that I may get away with a 530w small psu from be quiet! – specifically the pure power 530w one, which shaves 2cm off the height of the unit. We'll see, but thanks for posting this.

  4. Remko says:

    Nice article, very informative and useful.

  5. Huacanacha says:

    Ha, that's very similar to the build I currently have in progress:
    * Lian Li PC-Q08 in red
    * i5 2500 (not K)
    * Radeon 6850 – XFX dual fan

    But with a few variations:
    * Asus P8H67-I w/ USB 3.0, Wifi-N etc
    * 2x2GB G.Skill DDR3 1333 – laptop size to fit the MB
    * G.Skill Falcon Pro 120GB SSD – SandForce
    * Maybe my old 640GB hard drive for data
    * No DVD or BR
    * Stock cooler

    And an Antec 500W Neo-HE modular PSU that I already had on hand. This will be paired to my Samsung 46" C9000 LED TV, and take pride of place in my living area! Best thing is it's all for under $1k for a kick-ass mini gaming rig.

    So, I salute you on you're good taste ;)

    And as for the power requirements… component manufacturers tend to overstate PSU wattage requirements by a massive amount, in part because of cheaper PSU's don't come close to meeting their rated output. For a quality PSU you'd find it hard to build a system that needed more than a 400W unit, unless you get in to multi-GPU setups. A good quality, high efficiency, lowish output (400-500W) modular PSU is a good investment to make…

  6. Aussiedroid says:

    What did you use to measure the power usage. I would love to do this on my PC and find out how much it uses.

  7. Huacanacha says:

    AnandTech just reviewed a 300W PSU that the even the manufacturers suggest can be used with all bu the most powerful video cards… e.g. GTX460, Radeon 6950 etc. It's not modular, but otherwise sounds perfect for an ITX gaming build provided you can fit a full size power supply in your case:

    (page 2 for the video card mentions)

  8. Rictus says:

    I just discovered this website, and it has given me hope! I travel around the country for my job, and gaming laptops just aren't cutting it. expensive, and non-upgradable. I really want to build a small rig i can take with me. Thanks for the information :)

  9. zeldaman says:

    You may not need as big of PSU as you think, but I just want to mention that i've read that if you want optimal efficiency you should have a system drawing half the wattage of the maximum draw (or rating). i.e. 500W draw = 1000W psu

    • asr says:

      That's no longer needed if you have a 80Plus certified PSU, since it proves that the PSU can handle over 80% of efficiency at 20% load, 50% load or full load.

  10. ran says:

    hey there!
    first I msut say i'm very happy to found this site.. i've always thought if there are other people like me that like small enclosures with high gaming.

    now I have big dilema:
    I build new computer with this specs:

    iIntel Core i5-2500 Processor 3.3GHz 6MB Quad Core LGA1155 Box
    -Kingston‎ KVR1333D3N9/4G
    -Sapphire Radeon HD 6850 1GB GDDR5 PCI-E
    -Western Digital 1Tb Caviar Green 3.5 64MB SATA II
    -Zotac H67ITX-C-E Intel H67-B3 DDR3 LGA1155 DVI HDMI DP 7.1 USB3 eSATA ITX WiFi
    -Samsung SN-S083B Black Sata Slim Tray 8x DVD-RW
    -SilverStone Sugo SST-SG05 300W

    is the 300W psu that included with SG05 will be enough?
    im really worry about it.. and you gave me hope because the rig you built is pretty much the same..

    help me please! thx.

  11. Steve S. says:

    The builds are similar, but your chosen motherboard has onboard WiFi and I am not sure how much additional power it requires. As for the included 300w PSU, it has enough overall watts, but I don't know the full specs. The website says it has a dedicated 12v rail with 16 amps for a graphics card. As long as the second rail has 10 amps or more, you should be ok.

    But, just to be sure, why not got for the SST-SG05 450W? Same case and more than enough power for an ITX gaming rig

  12. ran says:

    thats a problem.. im from israel and this case not available att all.. (the 450W one).
    so that means i have no choice for now..
    the second rail of v12 has 14A (by silverstone) so it should be enough?
    and btw how my calculation say (14A+16A)*12V = 360W and thats not including the 3.3V and 5V
    how can it be?

  13. MattW says:

    I have a hd 4850 single slot in my Shuttle sa76g2 with a 240 regor and 4 gigs of ram. Most people thought i was crazy on its stock 250 wat psu but it worked like a charm. If i can run that a HD 5770 or that afox 6850 could run on the pc-60 300 watt shuttle psu. Good to see people who are willing to try and not just assume it cant work due to the size. BTW the shuttle case can only take a single slot card and without extra fans and that crappy stock heatsink it only get to 88c which people get in mid towers.

  14. Adam says:

    Hey Steve, reading this article makes me breathe a sigh of relief.
    I'm currently running a Gigabyte GTS 250, on a system with similar specs to yours listed here, but the PSU is a Thermaltake 430w. It's been running fine for a couple of years now, but I want to be able to play BF3 without splashing out on a new rig, and I'd been looking at the Radeon 6850…. I was worried I wouldn't have enough power, but it seems like I might be ok! Does this seem workable?

  15. Bleed says:

    Hey Steve,
    now im in the middle of a crossroad.
    i already have an acceptable midrange gaming rig, i5 2300 on z68, 4gb xms3 1333 with hd6870 and an intel ssd. n planning to transfer the relevant hardwares to a mini itx rig, using pc-q08 with gigabyte h67 mitx mobo. but its kinda big for an mitx case, n i kinda like em small.
    thus im also interested in the shuttle xpc SH67H3, equipped with a 300w 80+ bronze psu. i might undervolt n underclock both the gc n proc. but im afraid of the supposedly high power draw of my planned system will kill the psu on the long run, n shuttle's psu cant be easily replaceable using off the shelf aftermarket parts.
    will the 300w psu on shuttle able to handle the long-term power draw of my planned rig, or i should just skip the shuttle n build my rig using the lian li? any thoughts would be appreciated.
    anyway, im unable to comment using my facebook account. seems like theres something wrong with the page. you might wanna take a look at it.

  16. STEEL says:

    Gr8 post. But, i have a query.
    Im using Intel Q9550 2.8ghz, CoolerMaster 460W and ATI 6870 graphic card. Bt on my card help its mentioned to use minimum 500W, but my card is running fine. or Should I upgrate my Power supply ?

  17. Nadroj says:

    STEEL ur good with ur current PSU. Like you said its running fine and PSU is overstated by GPU mftrs

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