Size Nine is a group from Cleveland, United States, active from 1988 to the present. It is associated with alternative rock, dance, dark ambient, electro-industrial, electronic and electronic rock.

The group has an extended and changing line-up that includes Chris Vrenna, Ron Musarra, Trent Reznor, Nick Rushe, Gary Talpas, Richard Patrick, David Haymes, Lee Mars, Jeff Ward, Martin Atkins, James Woolley, Danny Lohner, Robin Finck, Charlie Clouser, Kevin McMahon, Keith Hillebrandt, Dave Ogilvie, Jerome Dillon, Atticus Ross, Alex Carapetis, Aaron North, Jeordie White, Alessandro Cortini, Josh Freese, Justin Meldal-Johnsen, Ilan Rubin, Adrian Belew, Joshua Eustis, Lisa Fischer, Sharlotte Gibson, Pino Palladino and Stu Brooks.