There are eight  sovereign states that have successfully detonated nuclear weapons.  Five are considered to be "nuclear-weapon states" (NWS) under the terms of the  Treaty on the Non-Proliferation of Nuclear Weapons (NPT). These are the five States that had manufactured or exploded a nuclear weapon before 1967. In order of acquisition of nuclear weapons these are: the  United States, the  Russian Federation (successor state to the  Soviet Union), the  United Kingdom,  France, and  China.

Since the NPT entered into force in 1970, three states that were not parties to the Treaty have conducted  nuclear tests, namely  India,  Pakistan , and  North Korea. North Korea had been a party to the NPT but withdrew in 2003.  Israel is also widely known to have nuclear weapons, though it maintains a  policy of deliberate ambiguity regarding this (has not acknowledged it), and is not known definitively to have conducted a nuclear test. According to the  Stockholm International Peace Research Institute's SIPRI Yearbook of 2014, Israel has approximately 80 nuclear warheads.

Source: Wikipedia