In this study, the roughness profile of a machined surface obtained via a flank milling process is thoroughly investigated through theoretical modeling and experimental demonstrations. First, the roughness profile of a machined surface generated by a single-tooth end milling cutter along a straight path is considered (without helical angle). The trajectory of a point on the cutting edge is constructed according to the cutting kinematics, and the roughness profile of the flank surface is theoretically extracted from the trajectory. The surface topography is constructed by integrating the roughness profile along the axial direction of the cutter. Based on the constructed roughness profile model, the effects of cutting parameters on the roughness profile are discussed, including those of the cutting speed, radial depth of the cut, and feed rate. In addition, the effects of cutter geometries including the cutter tooth number, tooth spacing angle, and helical angle on the roughness profile and surface topography are discussed. Further, roughness profiles are constructed for cutter feeds along different tool paths, such as round and curved paths. Finally, experiments are conducted to verify the method developed in this study. The results show that the roughness profile obtained from testing matches well with the theoretically modeled profile. Moreover, the methodology for constructing the roughness profile is compared to an existing approach, which shows that the method in this study is significantly faster.