Depending on how tight you like your shoes most downsize half to one and a half sizes from street shoe. I personally went down one and a half but I like my shoes really tight.

I went down one size, I use these for bouldering so I usually wear them for a couple climbs then slip them off for about ten minutes. I wouldn't recommend going that much smaller is you route climb, as for me, they would begin to hurt overtime. For bouldering I highly recommend.