Most of the available finite elements represent the stiffness matrix in terms of fixed equations, obtained for certain assumptions about the shape of the element and the distribution of elastic properties. Normally, prismatic elements with uniform material properties are considered. For non-prismatic elements, it is usually assumed linear or parabolic distribution of section properties along the element’s axis. However, modern technologies like 3D printing allow easier production of more complex shapes. In this paper, a general approach is proposed for stiffness matrix formulation of non-prismatic frame elements with arbitrary distribution of the elastic properties along the axis. For that purpose, the cross-section dimensions are represented by input functions both across and along the element. Then, the stiffness matrix is obtained in dependency of the input functions, instead of fixed parameters. This method is implemented as a short program in the engineering calculations platform Calcpad, and a simple example is elaborated. Then, the results are compared to SAP 2000 structural analysis software.