This website is ok:
http://www.extreme.outervision.com/psucalculatorlite.jsp it's not great but will give you a general guideline (Try and be as accurate and as detailed as possible). It says 366 W Recommended. Personally I would say go for 600w Plus. Always safer to go higher. Also buy a decent PSU. I have bought 2 shit PSU's in the past... (Died both times). Have fun!