Dense millimeter-wave networks are a promising candidate for next-generation cellular systems enabling multiple gigabit-per-second data rates. A major disadvantage of millimeter-wave systems is signal disruption by rain, and here we propose a novel method for rain sensing using dual-frequency measurements at 25 and 38GHz from a small-scale Tokyo Institute of Technology (Tokyo Tech) millimeter-wave network. A real-time algorithm is developed for estimating the rain rate from attenuation using both ITU-R relationships and new coefficients that consider the effects of the rain Drop Size Distribution (DSD). The suggested procedure is tested on measured data, and its performance is evaluated. The results show that the proposed algorithm yields estimates that agree very well with rain gauge data.