Nine states were required to ratify the United States Constitution under Article VII.
The requirement represented two-thirds of the 13 states then in the Union. Article VII stated that ratification by conventions in nine states would be sufficient to establish the Constitution among the states that approved it.
This rule differed sharply from the Articles of Confederation, which required unanimous approval for major changes. The Constitution therefore created a new framework rather than simply amending the old one. New Hampshire became the ninth state to ratify, on June 21, 1788.
Ratification did not immediately end political disagreement. Virginia and New York approved the Constitution soon after New Hampshire, while North Carolina and Rhode Island initially withheld approval. Rhode Island finally ratified in 1790. The nine-state threshold is an important example of how the framers balanced national effectiveness with state participation, and it explains why the Constitution could take effect before every state had accepted it.