Article VII of the United States Constitution required nine state ratifications for the Constitution to take effect.
The Constitutional Convention sent the proposed Constitution to the states in 1787. Article VII specified that approval by conventions in nine states would be sufficient, rather than requiring unanimous consent from all thirteen states.
New Hampshire became the ninth state to ratify on June 21, 1788, placing the Constitution into effect. The first state to ratify was Delaware, which approved it on December 7, 1787.
The nine-state rule was a major change from the Articles of Confederation, which required approval by all thirteen states for important amendments. Rhode Island, the final original state to ratify, did not approve the Constitution until May 29, 1790. This distinction often causes confusion between the number required and the eventual number of states that ratified.