This paper has the objective of characterising the macro and microscopic behaviour of Diesel sprays generated by a common-rail system and quantifying the influence of injection parameters and boundary conditions through a broad experimental study. The main purpose of this research is to validate and extend the different correlations available in the literature to the case of sprays generated by common-rail systems, i.e. at high injection pressures with small nozzle holes. The sprays are characterised in an environment which simulates the in-cylinder air density existing in the real engine when the injection starts. However, it should be pointed out that isothermal conditions at room temperature are considered and very little evaporation occurs. A wide parametric study has generated evidence needed to quantify the influence of the common-rail pressure, nozzle hole diameter and environment gas density on the spray tip penetration, spray cone angle and geometric volume of the spray, as well as the spatial and temporal evolution of drop size distribution. A theoretical analysis is made, and the results obtained are compared with the experiments of both this study and with those of the bibliography.