Coach, it is 9". but i just discover the new fan. I bought it at O.C aquatic 6" made by dayton. This fan can move massive amount of air (i mean crazy strong) @27w. My fans normally run all day during lighting period, since i replace my 2x9" black fan with the new fan. It only run 10-15 mins at the time. You can mount it inside your canopy..... If you need more info on the fan, please contact Kevin or Raskall311....