Separation of single wall carbon nanotubes (SWCNTs) by length via centrifugation in a high density medium, and the characterization of both the separated fractions and the centrifugation process are presented. Significant quantities of the separated SWCNTs ranging in average length from < 50 nm to ~ 2 microns were produced, with the distribution width being coupled to the rate of the separation. Less rapid separation is shown to produce narrower distributions; these length fractions, produced using sodium deoxycholate dispersed SWCNTs, were characterized by UV-Visible-near infrared absorption and fluorescence spectroscopy, dynamic light scattering, Raman scattering and atomic force microscopy. Several parameters of the separation were additionally explored: SWCNT concentration, added salt concentration, liquid density, rotor speed, surfactant concentration, and the processing temperature. The centrifugation technique is shown to support ten milligram per day scale processing and is applicable to all of the major SWCNT production methods: CoMoCat, HiPco, laser ablation, and electric arc.