This paper presents an electromagnetic modeling of a grounded metallic truncated cone to be used for calibration purposes of a microwave imaging system. The basic idea is to demonstrate the equivalence between the cone and a cylinder having a suitable radius, in order to simplify the computation of its capacity with respect to ground. A mathematical expression for the capacitance of the uniform cylinder is presented, and its validity is confirmed by comparing the data provided by this formula with numerical values given by a commercial simulator. Starting from this analytic result, the model of the cone is presented, and a procedure for the choice of the cylinder radius is discussed in detail. This methodology can be applied to calculate the contribution to the stray capacitance of a metallic tip used for scanning probe microscopy, and specifically for microwave sensing applications. In particular, the capacitance due …