The study addresses the issue of heterogeneous findings on optimized half divergence angle of micronozzles used for propulsion. The performance and flow characteristics are compared at two distinct operating conditions, i.e., when the flow is mostly subsonic and supersonic in the divergent section. Results show an optimum divergence angle and length, maximizing the performance for a specific operating condition and nozzle size. It is noted that the inconsistencies in literature is mainly due to exploratory efforts of small data sets. As the nozzle size decreases to the nanoscale, Re is very low, and the subsonic layer fully occupies the divergent nozzle section even at very high-pressure differences. The results show that the performance is significantly influenced by the wall thermal conditions. The study highlights the differences in flow behaviour between micro and nano-scale nozzles at various operating conditions. Based on numerical data obtained in this work, a new correlation is proposed to predict thrust per unit width for micronozzles.