The most widely used standard for measuring the power of nuclear
weapons is "yield," expressed as the quantity of chemical explosive
(TNT) that would produce the same energy release. The first atomic
weapon which leveled Hiroshima in 1945, had a yield of 13 kilotons;
that is, the explosive power of 13,000 tons of TNT. (The largest
conventional bomb dropped in World War II contained about 10 tons of
TNT.)
Since Hiroshima, the yields or explosive power of nuclear weapons have
vastly increased. The world's largest nuclear detonation, set off in
1962 by the Soviet Union, had a yield of 58 megatons--equivalent to 58
million tons of TNT. A modern ballistic missile may carry warhead
yields up to 20 or more megatons.
Even the most violent wars of recent history have been relatively
limited in terms of the total destructive power of the non-nuclear
weapons used. A single aircraft or ballistic missile today can carry a
nuclear explosive force surpassing that of all the non-nuclear bombs
used in recent wars. The number of nuclear bombs and missiles the
superpowers now possess runs into the thousands.