We report the static (epsilon(0)) and high frequency (epsilon(infinity)) dielectric constants of haematite (alpha-Fe2O3) as calculated using density functional perturbation theory. The values for bulk iron oxide are epsilon(11)(0) - 26.41; epsilon(33)(0) - 17.84; epsilon(11)(infinity) = 7.87 and epsilon(33)(0) = 7.57. The effective static dielectric screening of porous thin-films is predicted in aqueous solutions, using effective medium theory, to range between 33 and 44 depending on the crystal packing density. The large spread in literature values (12-120) can only be explained through surface and micro-structuring effects. These results will be important for interpreting and modelling the materials behaviour, particularly in electrochemical and photoelectrochemical cells. (C) 2013 Elsevier B.V. All rights reserved.