Who the nuclear powers are?

Official nuclear powers:

United States: According to the counting rules in the Strategic Arms Reduction Treaty (START), as of January 2009, the US had an estimated 5,200 nuclear warheads and 2,700 operationally deployed warheads.

Russia: Under the provisions of the START I, the Russian nuclear arsenal has been reduced to approximately 4,138 strategic nuclear warheads, as of July 2008.