The aim of this paper is to present a new projective stereological method that enables to estimate the size and the shape of a three‐dimensional convex object from measurements only made on its two‐dimensional projections. To do so, some geometrical and morphometrical measurements on the projected shadows of the three‐dimensional convex object are done and the value of the three‐dimensional convex object size and shape parameters are retrieved using the maximum likelihood estimation method. The proposed method is then applied to estimate three‐dimensional particle size distributions during crystallization processes.