Ratnasai is a village in Kumardungi tehsil in district of Pashchimi Singhbhum, Jharkhand, India. As per the data provided by Census of India in 2011, total population of Ratnasai was 291 which includes 141 males and 150 females. Ratnasai covers 1654.62 ha area. Pincode of Ratnasai is 833214.