You can find your answer by going to a PSU calculator like (www.extreme.outervision.com/psucalculatorlite.jsp) (www.coolermaster.outervision.com/) (support.asus.com/powersupply.aspx) or by selecting you PC parts on the pcpartpicker website.
But since you asked I did it for you (guessing you have 8gb of ram)
recommended was ~360
minimum psu watts was ~305
So I would say get a 430 watt psu minimum
You can go as high as you want, though that will just increase the price of the PSU. Incase you ever want to SLI here's a article on the power consumption (http://www.guru3d.com/articles_pages/asus_geforce_gtx_960_strix_2_way_sli_review,8.html) The total power consumption they got with a i7 3960, gtx 960 sli setup was 346 watts while stressed !!!! So you chose a efficient powerful rig.
Here are some psu's i'll recommend for your rig is cx 430 $40, FSP Group Raider S 550 $60 , SeaSonic 450W $70, CS450M $75
It'll be a waste buying a PSU with over 550w for your rig considering a sli setup consume less then 400 watts. Remember always buy a PSU with a 80+ rating and look at the reviews.