Based on the 2010 CDC report that showed 1,300,000 women were raped and 1,270,000 men were 'forced to peneotrate', and 2009 populations of 178.6 million females and 151.4 million males, the sexual assault rates for men are actually higher than for women.

Would be useful to get demographics for 2010, but 2009 is close enough. This is, of course, not taking into account prison rape, which increases the frequency of male rape even more. Given 80% of women raped men in the non-prison cohort, it's 1/148 men were raped by women.