To address this practical limitation, we present three different algorithms for predicting the nominal molecular mass of an analyte given only its EI mass spectrum and a reference library. The first algorithm attempts to quantify the likelihood that a molecular ion is contained in the mass spectrum, while the others leverage results from mass spectral library searching. These predictions can be used independently or as an ensemble (recommended) to infer the nominal molecular mass of the analyte. This manuscript is organized as follows. Section 2.1 provides a brief summary of mass spectral library searching, an integral component of two of the molecular mass prediction algorithms detailed in Section 2.2. Section 3.1 demonstrates examples of the algorithms in use and Section 3.2 discusses a performance study of the algorithms on presumed unknown analytes with spectra not contained in the considered reference library. A summary of our findings concludes the manuscript.