Redox reaction volumes for a series of iron complexes of the type Fe(L-L)(3-0-5),(CN)(x), where L-L is either 1, 10-phenanthroline or 2,2’-bipyridine and x = 0, 2, 4, or 6, have been measured using high-pressure cyclic staircase voltammetry. For these Fe(III/II) systems, where there are no significant bond length changes associated with the change in oxidation state, changes in the intrinsic volume for the complex ions are minimal and changes in the reaction volume therefore primarily reflect electrostrictive changes associated with the Fe(III/II) reduction. Estimates of the volume changes for individual Fe(III/II) half-cell reductions require an assignment of the molar volume change associated with the reference half-cell. From the charge dependence of the cell reaction volume for a series of Fe(III/II) reactions using a constant Ag/AgNO3 reference half-cell, we have estimated the reference half-cell volume change for the oxidation of Ag(s) to Ag+(aq) at 298 K and an ionic strength of 1.0 M to be -11.9 +/- 0.5 cm(3) mol(-1). The assignment is independent of any previously determined molar volumes for the reactants. Addition of supporting electrolyte, necessary for the electrochemical measurement and normal for most kinetic and mechanistic studies, has some effect on the volume changes.