if the conversion efficiency of the psu is 80% (it's actually better then that, especially with a 230V electrical system, but I don't have the numbers available).
http://www.plugloadsolutions.com/psu_reports/SILVERSTONE_SST-ST45SF_ECOS 2052_450W_Report.pdf
82.86% at "full load" (input = 534W, output = 442W)