The understanding of carrier transport in metal nanostructures is indispensable for the development of nanoelectronics. In particular, Pt nanostructures have been intensively studied to realize gas sensors based on adsorbate-induced surface electron scattering. Conventionally, electron scattering at the surface of metal nanostructures has been phenomenologically described by a single specularity parameter. In this work, surface electron scattering was quantitatively studied through molecular dynamics simulations, followed by density functional nonequilibrium Green’s function calculations. Although the extracted specularity parameters qualitatively agreed with empirically treated diffusive scattering at the O-covered Pt surface and specular scattering at the H-covered Pt surface, our atomistic calculation revealed an increase in resistivity owing to H adsorption on thin Pt(111) nanosheets.