PSU Watts And 12V Calculator



This PSU calculator can calculate both the wattage and 12V amps required to run your system. Data is based off measured values from any accurate manafacturer supplied data and the following sources:
Digit-Life, LostCircuits, SilentPCReview, StorageReview, TechReport, XbitLabs

 

Motherboard Chipset


 

Cpu

If your particular model isn't listed, pick a model with the same core as yours and use the change speed input to correct the speed to what it is. Use CPU-Z to find out what model cpu you have, and what core it is. It is perfectly normal for the default wattage to be a lot different from the the quoted TDP value of the CPU. The 'overclocking' feature can also be used for undervotling / underclocking your cpu if required.


 

 

Override default wattage:

Default voltage:

Default speed (GHZ):

Default wattage:
Change voltage:

Change speed (GHZ):


 Overclocked wattage:

 

Graphics Card



Number of graphics cards (SLI/Crossfire)

 
Default core speed (GHZ):

Default memory speed (GHZ):

Default wattage:

Change core speed (GHZ):

Change memory speed (GHZ):

 Overclocked wattage:

 

Dram

Memory voltage is typically 1.5V for DDR3, 1.8V for DDR2, 2.6V for DDR. Memory speed is typically 1066 for DDR3, 533 for DDR2, 400 for DDR1, obviously both of these are different when overclocking.

Number of sticks of ram:

DDR or DDR2/3?:

Memory Voltage:

Memory Speed:

 

Drives

For optical drives, choose 'None' option if not applicable.

Hard drive type 1:



Number of drives:
 
Hard drive type 2:



Number of drives:


Optical drive 1:


 
Optical drive 2:


 

MISC

Number of PCI cards:

 Number of low power (100mA) USB devices (usb sticks, mouses etc):

Number of high power (500mA) usb devices (unpowered external hard drives mainly)

 Sound Card Model:

 

Cooling

If your case fan model isn't listed, it can be manually entered from manafacturer data, for example: this fan has a draw of 0.12A, while this fan has a power draw of 2.46w (convert to amps by dividing by 12. eg. 2.46W / 12V = 0.205A).

Case fan (type 1) 12V amps draw

Number of fans:

5V modded?

 
Case fan (type 2) 12V amps draw



Number of fans:

5V modded?



For water pumps and other extreme cooling methods, this data can be manually entered from manafacturer data as well, for example this Switftech pump uses 2A.

Water pump / peltier 12V draw (amps):


 

UPS features

NOTE: If your confused by any of the terms here, leave them on default values.

These factors merely influence the UPS calculations, they did not in anyway influence the size of the psu required. This includes psu efficiency - psu's are rated by dc output (unchanged by effeciency), not what they draw from the mains (influenced by efficiency). If you have any other devices connected to the UPS on top of the PC and monitor, add up their power draw and include it in the 'other devices watt draw' field. If your monitor has a power draw listed in its specifications, use that instead of the suggested value. The UPS power factor is its rated wattage divided by its rated VA, so for example a 350W / 500VA UPS has a power factor of 0.6, as does a 600W / 1000VA UPS. If this is not specified, assume its 0.6. The psu pfc type refers to if the psu has any sought of power factor correction, usually 'none' for cheaper models while higher end models have active power factor correction.

PSU pfc type

 PSU efficiency at load

 UPS power factor

Monitor

Other devices watt draw

 



Actual System Power Consumption

This is how much power the computer will actually be using off the psu while gaming. Obviously both of these should be well under what the psu is rated for. See the recommended size PSU at the end to work out how big a PSU you need, after taking care of the 'dual rail psu checks'.

Max sustained total power consumption while gaming (watts)

3.3V / 5V / 12V combined amps while gaming


This is full hard drive (all drives) and CPU activity, perhaps a 'worst case' load for fileservers.

File Server full backup watts

File Server backup 12V combined amps

 

Recomended minimum UPS Ratings

Use these values to work out how big an Uninteruptable Power Supply (UPS) you need to ensure your pc stays powered during blackouts. It is importent to note that the specs of UPS needs to exceed both the watt and VA (volt amp) ratings given here.

  Computer Only Total (inc monitor etc)
Actual AC Watts drawn from wall outlet
Actual VA draw
Recommended Watts UPS rating (Watts / VA)  

 

Multiple 12V Rail PSU Checks

These calculations are based on the typical configuration of a ‘by the books’ dual 12V rail psu, that is cpu gets 12V2 to itself, and everything else is on 12V1. Multiple (3,4,5 etc) 12V rail psu's vary a lot in configuration, so have not been coded for, instead go off the guideliness below. Note that regardless of what the PSU label says, the capacity of each individual 12V rail is at least 18-20A, sometimes more but almost never less. Also some newer psu’s have no split rails at all (ie only has one big 12V rail) such as new Seasonic built psu’s (despite being labelled as having multi 12V rails).  Additionally, if any of this numbers are quite high (say more than 30A) you'll need to either research carefully on the rail distribution, or get a single 12V rail psu in order to avoid shutdowns.

General guidelines to pick a good rail distribution on multi 12V rail psu's (don't apply to rails rated for >25A rather than the normal 18-20A):
* No more than 1 6pin pcie on the same rail as the 24pin atx connector
* No more than 1 6pin pcie on the same rail as an EPS or ATX12V connector
* No more than 2 6pin pcie on any other rail (and no 8pin pcie).
* No more than 1 8pin pcie on any other rail (and no 6pin pcie).
* No more than a couple of hard drives on a rail that already has 2 pcie / 1 8pin / atx connector on it
* No more than roughly 7 hard drives on a rail that is otherwise free

Typical Gaming 12V1 draw If this exceeds 18A, a dual 12V rail psu probably won’t work - psu will shut down while gaming. The only solution is to buy a non dual 12V rail psu*.

Startup 12V1 draw If this exceeds 18A, you may have issues with a dual 12V rail psu thats ‘by the books’. If your motherboard supports ‘staggered spinup’ (SATA only) that should also help solve this issue. Don't be overly concerned if the recommended 12V combined amps ends up being very close to this, as its a peak draw that only lasts a second or two (as apposed to gaming 12V draw which is continuous and therefore a lot more stressful on the PSU).

Peak CPU (12V2) draw High end overclocked cpu's can draw over 18A, so if it does a PSU with EPS connector or one that is actually single 12V rail is required.

* A dual 12V rail psu can often work with more than 18A power draw if it puts the second graphics card on the same 12V rail as the cpu (12V2), like the Silverstone Element 500w, very few do this however. Alternatively if the current limiters are set to more than 20A (eg. Enermax liberty 500w), or there aren't any (eg. just about any Seasonic) then a dual 12V rail psu will work, but in the majority of cases it won't, regardless of 12V combined amps and wattage rating of the psu.


Recommended Minimum PSU Ratings

When choosing a psu make sure both the wattage AND 12V combined amps (given as amps and watts here since some PSU models quote the figure as amps, and others as watts) are met. See the OCAU PSU Wiki for a guide on how to work out 12V combined amps. When sizing a recommended psu, its not a disaster if the calc says you need a 403w psu and you've got a 400w, it'll still work as long as the psu is decent brand/model as there is plenty of 'headroom' in these calculations. See the OCAU PSU Wiki for a list of what brands are classed as 'generic' and what are decent brands. Even amongst brands, some models are better than others, so reading up reviews on candidate PSU's is a good idea to ensure you have a decent PSU. Also its perfectly normal for the recommended 3.3V and 5V ratings to be very small (they will be except for older systems), this just indicates that the psu you use doesn't need to have high ratings on these rails.

Recommended PSU wattage for generic brand PSU:

Recommended 12V combined amps for generic brand PSU:

 

Recommended PSU wattage for decent brand PSU:

Recommended 12V combined amps / watts for decent brand PSU:

 

Recommended 3.3V Amps

Recommended 5V Amps

Recommended 3.3V/5V Combined Watts



 

 



This is a work in progress, send any feedback / suggestions to SnooP(at-)aanet.com.au

Legal bs: This is a guide only, I take no responsibility if you buy a psu that destroys your system based on any information here.