Ratan Sar is a village in Chhatapur tehsil in district of Supaul, Bihar, India. As per the data provided by Census of India in 2011, total population of Ratan Sar was 6,700 which includes 3,485 males and 3,215 females. Ratan Sar covers 633 ha area. Pincode of Ratan Sar is N/A.