As the dimension of copper interconnect scales into the nano-meter regime, the resistivity of copper rapidly increases, primarily due to an electron scattering effect and other dimensional dependent factors, such as film quality. In this paper, we attempt to use a simplified parameter, dimension impact factor (DIP), which includes both surface and grain boundary scattering, to characterize the dimensional dependency of metal resistivity. Among the metal studied, silver has the largest DIP while aluminum has the lowest value. The chief reason is that aluminum has a short electron mean free path (MFP), meaning that it tends to be less affected by dimensional scaling, and has a higher electron specular ratio. In addition to the factor of MFP, resistivity can be affected by other dimensional dependent factors, such as film quality.