I was randomly browsing through the net when I found this site
The power of a nuclear war-shell as possessed in the arsenal of countries. If we see below, it is a comparison in terms of Mega tons (unit to measure explosive potential)
The Most Powerful Bomb Ever Constructed
On October 30, 1961, the most powerful weapon ever constructed by mankind was exploded over the island of Novaya Zemlya in the Arctic Sea. The device was code-named “Ivan,” and it was a multi-stage hydrogen bomb which was built in only fifteen weeks by engineers in the USSR, using off-the-shelf nuclear weapon components.
Ivan– sometimes referred to as “Tsar Bomba” or “King of Bombs”– was originally designed to yield a 100 megaton explosion, but the soviets decided that such a blast would create too great a risk of nuclear fallout.Even at half strength, Ivan was so powerful that it was completely impractical. Much of the explosion’s energy radiated upwards into space, and that which didn’t was so excessive that using the device on any populated targets world would have resulted in adverse effects on Russian interests.