5113 Number of operational warheads in the U.S. nuclear stockpile, according to the Pentagon. That figure is down from a peak of 31,225 weapons in 1967. Bulletin of the Atomic Scientists estimated in 2009 that Russia has 4,830 operational warheads; the Soviet arsenal topped out at around 45,000 weapons in 1986. The new Strategic Arms Reduction Treaty would limit both countries to 1,550 operational warheads each.

111 Estimated number of nuclear weapon storage sites worldwide, according to the International Panel on Fissile Materials. Russia has the most, with 48; the United States is second, with 15 domestic and 6 foreign sites. The total number of nuclear weapons worldwide is approximately 20,350, with about half of those operational.

0.1 Approximate percentage of the mass of a uranium atom converted to energy during nuclear fission. The amount of matter converted to energy in the atomic bomb dropped on Hiroshima was about 700 milligrams, less than one-third the mass of a U.S. dime.

6.3 x 1013 Estimated energy, in joules, released from the Hiroshima bomb, the equivalent of 15,000 tons of TNT. At low altitudes, about half the energy of such a bomb is released in the air blast, 35 percent as heat and 15 percent as nuclear radiation. The fireball resulting from the Hiroshima explosion was 50 percent hotter than the surface of the sun.

55 Pounds of weapons-grade uranium required to build a nuclear weapon. The global stockpile of highly enriched uranium stands at around 1,600 tons, enough for more than 60,000 nuclear weapons. Another 60,000 could be constructed from the 500 tons of separated plutonium estimated to exist in stockpiles around the world.