That calculator is miles out. No wonder people end up recommending huge psu's. According to that my rig draws 467w. 197w more than it actually draws!! What a load of rubbish.
actually did calculation with according to what i see from your specs, guessed a couple of devices USB, 3 fans and 2 HDD and it comes to 369w

PS a dual core is a single socket - I think you put dual socket that is why you got results.
anyway it's a tool to estimate and i find it useful, if you know of another toold to estimate that is better than please share with us