Abstract Mass transfer correlations to a carbon or graphite felt flow-through electrode have been established using two electrochemical reactions: [Fe(CN) 6] 3− /[Fe(CN) 6] 4− and Hg 2+/Hg 0. The correlations a* k m vs v obtained with hexzcyanoferrate were reproducible and independent of electrode thickness. Correlations established for mercury demonstrated that mass transfer to the felt was lower and varied with felt thickness. Variation of actual specific electrode area with the electrochemical reaction concerned and the nature of felt surface may explain these phenomena. It is proposed that mass transfer studies to flow-through electrodes should be backed by a study of the specific electrode area in the same electrochemical conditions.