Emulsions are used as delivery vehicles for many active and functional chemical ingredients. There is an increasing need for developing new ways of producing emulsions on demand having desired critical quality attributes. Hydrodynamic cavitation (HC), which is a process of generation, growth and collapse of vapour cavities leading to intense localised shear and energy dissipation, offers an attractive platform for producing emulsions. In this work, we present experimental and computational results of a breakage of a single oil drop injected in a HC device. A single drop of oil was injected in a continuous stream of demineralised water flowing through a vortex based HC device. Tween 20 surfactant (2%) was used to prevent coalescence. The droplet size distribution (DSD) at the outlet of HC device was characterised using the imaging method. A detailed 3D computational model was developed to simulate turbulent cavitating flow through the considered HC device and resulting drop breakage and droplet size distribution. The developed model was used to quantitatively relate Sauter mean diameter (d32) and droplet size distribution (DSD) at the outlet with the operating parameters of the HC device. A single-pass through the vortex based HC device was able to bring down droplet size from ∼103 µm to ∼101 µm. The data and the model discussed in this work will provide a systematic basis for developing models, cavitation devices and operating protocols to produce emulsions with desired DSD.