yes see how much wattage every component needs add them up and add a extra 50 watt due to the loss of true output from the power supply and there you go.even with 2 gpu you whould not need more than 850 watt if every gpu requires 250 watts each.
what is your configuration?
At the moment I have a Raidmax-1000AE 1000 watt PSU. The reason that I got it was because I didn't know how much power that I needed.
Is there any way to accurately calculate what wattage PSU that I need?
You're asking the wrong question, Watts is irrelevant. What's important is how many amps your PSU can supply on the 12 volt rail (this will be published on the manufacurers website and also be shown on a sticker ont he supply itself) vs how many amps your components require.
You can work amps out easily using the equation Watts = Amps x Volts. Volts is always 12 and the watts are published by the manufacturers (usually referred to as the TDP or thermal design power).
we usualy say how many watts do need not how many amps.
if you go http://ark.intel.com/products/75121/Intel-Core-i7-4765T...
you will see down
Max TDP 35 W.not amps.
then there is not only 12 volts.there 3,3v 5 v and -12v
for the storadge only he will need that equasion to conver it to watts.
we pay watts to the power companies not amps.if you chance the voltage whie having the same ampradge you whould have difrent wattage.wattage is the universal power consumption refrence.
But as stated the current capability is the important spec. PSU Wattage specs are a grand total - for GPUs the main concern is the 12 V Rail. Good quality PSUs(NOT RTAIDMAX) is what you need to look for. Check out JonnyGURU.com and read a little while.
Because the total Wattage of a PSU is not broken down for the consumer - Amps are what you need to look at - end of story. Some of us know how to do calculations for current voltage and power but all GPUs need a powerful 12V supply and the important spec is how much current on the 12v rail - not the total power of a PSU!!!
Edit: BTW good example gopher 36A VS 54 Amps on the 12V Rail - I would pick the Seasonic 650W!
It can be confusing and many people do not understand specs. It's like an in dash car stereo putting out 200W - Bull$hit!!!!. Most gpus have power recommendations inflated because many people do not understand that they need sufficient 12V current. GPU manufacturers just give a larger power requirement so that most psus (even crappy ones) will run their hardware. Again I restate - the important spec for gpus is the current capability on the 12V rail - not the total power in Watts of the power supply assuming the rest of the voltage rails have enough power for the rest of the sytem.