We present regional earthquake magnitude conversion relations among different magnitude scales (, , , , and ) for the Himalayan seismic belt developed from data of local, regional, and international seismological agencies (International Seismological Centre [ISC], National Earthquake Information Centre [NEIC], Global Centroid Moment Tensor Solution [CMT], International Data Centre [IDC], China Earthquake Administration [BJI], and National Centre for Seismology [NDI]). The intra‐ (within the same magnitude scale) and inter‐ (with different magnitude scales) magnitude regression relations have been established using the general orthogonal regression and orthogonal distance regression techniques. Results show that the intra‐magnitude relations for , , and reported by the Global CMT, ISC, and NEIC exhibit 1:1 relationships, whereas reported by the IDC, BJI, and NDI deviates from this relationship. The IDC underestimates and compared with the ISC, NEIC, and Global CMT; this may be due to different measurement procedures adopted by the IDC agency. The inter‐magnitude relations are established between and , , and reported by the ISC, NEIC, IDC, and NDI, and compared with the previously developed regional and global regression relations. The duration () and local () magnitudes reported by NDI exhibit a 1:1 relationship. The derived magnitude regression relations are expected to support the homogenization of the earthquake catalogs and to improve seismic hazard assessment in this region.