Ratan Sagar is a village in Patahi tehsil in district of Purba Champaran, Bihar, India. As per the data provided by Census of India in 2011, total population of Ratan Sagar was 1,933 which includes 1,040 males and 893 females. Ratan Sagar covers 137 ha area. Pincode of Ratan Sagar is 845427.