Here's a thread with some pictures of the mini 160 showing the overall dimensions:
http://reefcentral.com/forums/showth...&highlight=160
I have mine in a space that is 12" x 11" with a 9" water height. I also have a heater and my 3 return lines in there though so it's a snug fit and as i have crabs mentioned you don't want to have the intake too close to any side of the sump.
If you end up getting a 180 make sure you get a gen 2 with the enlarged volute - some retailers are still selling gen 1 models unfortunately.