Nine state ratifications were required for the United States Constitution to take effect.
Article Seven established the Constitution’s ratification rule: approval by conventions in nine states would be sufficient to establish the Constitution among the states ratifying it. This threshold was a compromise between requiring unanimous approval and allowing a simple majority of all thirteen states.
New Hampshire became the ninth state to ratify on June 21, 1788. That decision placed the Constitution into effect, although major states including Virginia and New York ratified afterward. North Carolina and Rhode Island also waited, so the new government initially operated without unanimous approval from the original states.
The rule is often confused with the total number of original states, which was thirteen, or with the number of delegates who signed the document. Those figures describe different parts of the founding process. Article Seven concerned state conventions and the legal condition needed to launch the new federal system.