Karhana registered a personal best of 20.04 metres to cross the 20-metre qualifying mark for the London Olympics and the World Championships to be held in Daegu, South Korea from August 27.
The earlier personal best of the 24-year-old lad, who is now training in Hungary, was 20.02 metres which he registered at the 2009 Inter-State Athletics meet in Chennai.
Karhana had finished third in the Asian Championships at Kobe, Japan earlier this month. Defending his shot put title, he managed a bronze with a season's best of 19.47 metres.