Vertical Scanning Interferometry (VSI) may induce optical artefacts in surface topography measurements. The influence of these optical artefacts on the calculation of Rk surface roughness parameters, contact stiffness and flow factors were studied. Two surface measurement techniques were used: Atomic Force Microscopy (AFM) and VSI. Calibration grids were used to make it easier to isolate the causes of these artefacts, while a real engineering surface was used to compare these two techniques in an industrially applied case. It was found that the optical artefacts have a large influence on all the roughness parameters, contact stiffness and flow factors calculated on the calibration grids. However, for the engineering surface the differences between AFM and VSI measurements were much smaller. ► Comparison undertaken of VSI and AFM measurement techniques. ► Silicon ‘calibration’ grids and a ‘real’ surface measured. ► Roughness parameters, contact mechanics and flow factors investigated. ► VSI artefacts significantly influence results for surfaces with extreme geometries. ► However, VSI found to be sufficiently accurate for a typical engineering surface.