Optical calorimetry was recently presented to be a versatile screening technique for a rapid and simple evaluation of adsorption properties (e.g. specific surface area, adsorption capacity) of porous materials. In this study, optical calorimetry is introduced for the sizing of nanoparticle powders. For this purpose, the sizing is done with various pyrogenic nanoparticles (SiO₂, TiO₂, Al₂O₃, ZnO, WC) in a diameter range of 6–100 nm. By comparing the results of optical calorimetry to reference physisorption measurements as standard nanoparticle sizing technique, an excellent correlation is demonstrated. In contrast to the standard physisorption method, the optical calorimetry allows a simple and rapid screening (only 5 min per sample) of nanoparticles and therefore is well suited in fields with high sample numbers such as high-throughput synthesis or process control.