The paper deals with an assessment procedure of the maximal electromagnetic field values. The technique used in this work comprises the multiquadric approximation of a field quantity obtained using the discrete measured data set. The approximation sufficiently handles multidimensional multiextreme functions by interpolating their discrete values accurately. Subsequently, the maximal value of a field quantity is evaluated by minimizing the negative multiquadric approximation via a stochastic optimization method - differential evolution. Therefore, the implemented procedure provides the maximal value assessment on the basis of a limited number of measured values, thus reducing the experimental cost.