How many square miles did the Louisiana Purchase add nominally to the United States in 1803?

The Louisiana Purchase added approximately 828,000 square miles to the United States in 1803.

The United States bought the territory from the French First Republic for $15 million. The agreement covered most of the Mississippi River drainage basin west of the river, although France had limited control over many areas inhabited by Native American nations.

President Thomas Jefferson wanted access to the Mississippi River and the port of New Orleans. Negotiators Robert Livingston and James Monroe were initially seeking New Orleans and nearby territory, but French officials offered the much larger region. The deal nearly doubled the nominal size of the United States.

The purchase included all or part of 15 present-day U.S. states and parts of two Canadian provinces. Its exact boundaries were later clarified through agreements with Spain and Britain. The commonly cited 828,000-square-mile figure describes the nominal area acquired, not land that was empty or unclaimed.