52"

I have 44" in my smaller rooms and 52" in my larger rooms. The 44" seems to work well enough it depends on how you want it to look on the ceiling. 52" looks quite a bit bigger in a small space.

My son had this size room and we went with a 52" fan blade. First the fan will cool the room better. A smaller fan will have to be on high all the time and still not work as well. Also a fan on high is noisier than medium. You can ask Home Depot or Lowes this question by phone or in person.