I suggest you go with a half size larger than you normally wear.

All my Bass dress shoes are a size 11.  I went ahead and bought these Clark's in a size 11 and 11.5 knowing I could try them both and return the other.  The shoe is somewhat narrow at the toes so 11 was too tight but 11.5 fit just fine.  The toe sticks out a little more because of it, but I have not found it at all uncomfortable or sloppy like you would when you wear shoes that are too large for you.