The purpose of this work is to estimate the mean volume radius (Rmvr) from in-situ and remote sensing observations collected during the Alliance Icing Research Study (AIRS) which took place over the Ontario and Quebec regions in the winter of 1999-2000. Earlier studies have shown that determining the size of super-cooled large droplets in an icing environment is important for aircraft safety studies. Measurements of droplet number concentration (Nd), liquid water content (LWC), Doppler velocities (Vd), liquid water path (LWP), temperature (T), and cloud physical thickness (dz) were used to obtain Rmvr profiles from four different methods for two cases. One of the methods was based on a relationship between Doppler velocities and Rmvr, and the others were related to microphysical parameters. In the calculations, both Nd-T and LWC-T relationships developed earlier were used for obtaining Rmvr. Then, the calculated results were compared with in-situ observations.