The "kiloton (of TNT)" is a unit of energy equal to 4.184 terajoules.
The "megaton (of TNT)" is a unit of energy equal to 4.184 petajoules.
A gram of TNT releases 2673–6702 J (joules) upon explosion. The energy liberated by one gram of TNT was arbitrarily defined as a matter of convention to be 4184 J, which is exactly one kilocalorie, which is the approximate amount of energy needed to raise the temperature of one kilogram of water by one degree Celsius at a pressure of one atmosphere.
The Little Boy atomic bomb dropped on Hiroshima on August 6, 1945, exploded with an energy of about 15 kilotons of TNT (63 TJ), and the Fat Man atomic bomb dropped on Nagasaki on August 9, 1945, exploded with an energy of about 20 kilotons of TNT (84 TJ). The modern nuclear weapons in the United States arsenal range in yield from 0.3 kt (1.3 TJ) to 1.2 Mt (5.0 PJ) equivalent, for the B83 strategic bomb.
The energy contained in one megaton of TNT (4.2 PJ) is enough to power the average American household for 103,000 years. The 30 Mt (130 PJ) estimated upper limit blast power of the Tunguska event could power the aforementioned home for just over 3,104,226 years. To put that in perspective, the energy of that blast could power the entire United States for 3.27 days.
The total energy of all explosives used in World War Two (including the Hiroshima and Nagasaki bombs) is estimated to have been three megatons of TNT.
Approximate total yield of the 1980 eruption of Mount St. Helens: 28 TWh, 24 MT TNT.
Not listed: effect on Miami, Savannah, Norfolk, Baltimore, the Dominican Republic, the Turks and Caicos and the entire NE coast of South America of setting off a nuke deep inside the slip-fault on La Palma.