The calculations of electronic g-tensors, one of the most important parameters in electron paramagnetic resonance spectroscopy, are carried out for dangling bonds ( DBs ) introduced into hydroxylated and aminated diamond nanoparticles, or nanodiamonds ( NDs ) , of different shapes and sizes. Regarding the shapes of NDs, octahedral, cubic, and tetrahedral model systems are used, while the impact of the change in size is inspected by increasing octahedral ND from C 35 to C84. The results for single DBs reveal that tetrahedral NDs exhibit the widest variation range of the isotropic g-shift values for both surface functionalization schemes, whereas the isotropic g-shifts of octahedral and cubic NDs tend to strongly overlap. On the other hand, if one treats NDs as an ensemble of nanoparticles constituting a sample, the isotropic g-shifts arithmetically averaged over all available DBs show that tetrahedral ND with hydroxylated surface possesses a significantly higher value than the rest of the considered systems. However, applying the Boltzmann distribution results in a substantially lower value for cubic ND. In contrast, aminated NDs do not demonstrate average values that stand out from the others, irrespective of the analysis method employed. Overall, in addition to the comprehensive magnetic properties, the obtained data also provide interesting details on the formation of DBs in hydroxylated and aminated NDs.