Nine states had to ratify the United States Constitution before it could take effect under Article Seven.
The Constitutional Convention sent the proposed document to the states in 1787. Article Seven specified that ratification by conventions in nine states would establish the Constitution among the states approving it, rather than requiring unanimous approval from all thirteen.
New Hampshire became the ninth state to ratify, on June 21, 1788. That vote put the new constitutional framework into effect, although several states had not yet ratified. Virginia and New York followed soon afterward, while North Carolina and Rhode Island joined later.
The requirement is sometimes confused with the total number of original states. Thirteen states ultimately ratified the Constitution, but Article Seven required only nine for it to become operative.