The Constitution merely declares that new states cannot be created by merging or splitting existing states without the approval of both the U.S. Congress and the states' legislatures. Otherwise, Congress is given the authority to determine the conditions for statehood.

Do the states have to ratify a new state?

New States may be admitted by the Congress into this Union; but no new State shall be formed or erected within the Jurisdiction of any other State; nor any State be formed by the Junction of two or more States, or Parts of States, without the Consent of the Legislatures of the States concerned as well as of the ...

What vote is needed for statehood?

A simple majority in each House of Congress is required to pass statehood legislation, however, in the United States Senate the filibuster requires 60 votes to invoke cloture. Some statehood advocacy organizations have called for amending or abolishing the filibuster as a path to achieve statehood.