Nine states had to ratify the U.S. Constitution before it could take effect under Article VII.
The Constitution’s framers chose approval by state conventions rather than by the existing state legislatures. Article VII stated that ratification by conventions in nine states would establish the Constitution among the states ratifying it.
New Hampshire became the ninth state to ratify, on June 21, 1788. That vote met the constitutional threshold, although New York and Virginia had not yet ratified. Their eventual approval was politically important because both were large and influential states.
Rhode Island was the last of the original 13 states to ratify, doing so on May 29, 1790. The nine-state rule did not mean that all states had to agree before the new government could begin. It allowed the Constitution to become operative among the ratifying states, while the remaining states decided whether to join.