Working out needed psu size?

freebooter

freebooter

freebooter

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I am looking at getting a new psu and I am not sure what size I need. Rather than just ask for recommendations I wondered if there is a way of calculating it. I assume it is just a matter of adding up the loads of everything in pc and then getting a psu powerful enough to cover it.

It is easy to get the power of a cpu and graphics cards aren't too bad although nvidia gives figures whereas ATI just seem to give a recommended size of psu but the info can usually be found on reviews. However I don't know how much power the other components need, ie

motherboard (in addition to cpu)
ram (is power used set by size or no of sticks)
hard drives & ssd
optical drives
fans
extra cards pci etc
plugin devices ie usb etc

Perhaps if this info could be sorted then it could be made into a sticky so people could work out what they need themselves rather than keep asking for recommendations?

thanks
 
Some components vary considerably, such as motherboards and CPUs. Hard drives use about 5w and RAM about 1w per stick. SSDs use fractions of a watt, even when active.

Fans also vary but 5w each for a typical speed fan is ample to be used in calculation.

Not sure what PCI cards use but wouldn't have thought it'd be much more than a few watts even for a RaID card or similar. Soundcard may be slightly more I guess.

A USB device can use no more than 5v at 500mA so a max of 2.5w, although it will usually be less.
 
Unless your in to very heavy overclocking and or crossfire/sli its usually much less than you think. (as per Tealcs comments above after CPU and Graphics the rest of the system will be well under 50w)

CPU and Graphics are the significant elements and the newer generations are at least staying at similar levels of power usage or getting lower with each generation.

A good quality 600 ish watt power supply will drive any of the current chips with any graphics card and it will I am sure also handle the next generations of cpus and graphics cards.

I am of the opinion at the extra cost spent on more expensive PSUs and cooling for SLI/crossfire is better spent on single graphics card solutions and gives much less in potential problems.
 
To give a rough idea my system (in sig) with custom water and several hard drives pulls 500w from the mains with Prime & Furmark running together.
 
Single GPU 450w+ Crossfire / SLI 700w+
Go for an 80%+ PSU from a rated manufacturer.
Add 100-150w to above for a comfort factor if you wish.
 
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