The present work deals with the estimation of average floe diameter using sedimentation and optical data. This study was applied to a kaolin suspension destabilized by chemical dosing with iron salts (FeCl3 or FeSO4) or electrocoagulation (EC) with iron electrodes. Optimum pH and coagulant concentration were defined by turbidity measures on destabilized suspensions. The suspensions were subsequently settled in a vertical column. Critical heights of sedimentation delimiting hindered settling and consolidation ranges were estimated when plotting data of settling rate of the suspension-supernatant height as a function of time. Average floe diameter and density were assessed considering the Richardson and Zaki model in the hindered settling range. Floe images obtained by optical microscopy allows us to check the relevance of the floe sizing derived from sedimentation data. Eventually, the estimated size and density of floes generated by EC and chemical dosing techniques were compared. (C) 2003 Elsevier Science B.V All rights reserved.