Article Seven required nine state ratifications for the U.S. Constitution to take effect.
The Constitution was submitted to state ratifying conventions rather than simply being approved by existing state legislatures. This procedure reflected the document’s claim to establish a new federal system based on the authority of the people in the states.
The ninth ratification came from New Hampshire on June 21, 1788. At that point, the Constitution became effective for the states that had ratified it, even though four original states had not yet approved it.
All 13 original states eventually ratified. Rhode Island was last, approving the Constitution on May 29, 1790. The nine-state rule is therefore different from the total number of original states and from the unanimous approval used by some states.