Local Volta potential differences (Delta psi) between a platinum coated AFM tip and various pure metal specimens with a thin humidity induced surface electrolyte layer have been determined via scanning Kelvin probe force microscopy (SKPFM). SKPFM derived Delta psi display a linear correlation with the same quantities obtained under nominally identical environmental conditions using a scanning Kelvin probe (SKP); the slope is within experimental error one. By exploiting this correlation and using a SKP previously calibrated versus a series of metal/aqueous metal ion redox couples it is possible to indirectly calibrate atmospheric SKPFM derived Delta psi with electrochemical potential. Good correlation is also obtained between immersion corrosion potential (E-corr) in NaCl electrolyte and SKP determined Delta psi in the presence of a NaCl dosed humidity layer. This implies that SKPFM may be calibrated directly against immersion E-corr provided SKPFM measurements are performed under suitably controlled conditions of atmospheric relative humidity and surface electrolyte dosing. (C) 2012 Elsevier Ltd. All rights reserved.