The present work investigates the hydrodynamic cavitation (HC) performance of vortex-diode based devices, which show early inception and superior cavitational performance compared to conventional devices. The study provides novel data on the cavitational efficiency at different operating pressures for two sizes of cavitation devices, addressing a gap in the literature. Using coumarin as a chemical dosimeter in acidic conditions, the study tracked the formation of 7-hydroxycoumarin (7OHC), a hydroxylation product of coumarin, to evaluate cavitational performance. Optimization of solution pH and initial concentration led to selecting pH 3 and a 15 ppm concentration for subsequent experiments with two vortex-diode devices of 12 mm (D12) and 6 mm (D6) diameters. These devices were tested under various pressure conditions. The formation of 7OHC was analyzed in relation to process time, number of passes, and a characteristic number of passes (n*) – which correlates device dimensions with operating velocity. The results indicated that the D6 device outperformed the D12 in terms of efficiency at inlet pressures ranging from 100 to 400 kPag. Analysis of 7OHC formation trends with respect to n* revealed that while there were variations within different pressures for a given device, the performance was comparable across different scales. By keeping a constant n* across varying pressures (P1 = 100 to 400 kPag and P2 = 0 to 300 kPag), the study observed comparable 7OHC formation across different operating conditions and scales. This data is vital for selecting suitable scales and conditions for HC devices and for validating multi-scale models in this field.