Crystal nucleation of single micro-sized tin droplets was investigated by in-situ experimental studies during rapid heating-cooling processes at rates up to 4 × 10^4 K/s. A theoretical model of these processes was developed on the basis of the classical heterogeneous nucleation theory and advanced then by a cavity induced heterogeneous nucleation model and cavity size dependent growth. It allows one to describe the cooling rate, droplet size and prior liquid overheating effects on crystal nucleation in single micro-sized tin droplets.