Approximately how large was the Louisiana Purchase in square miles?

The Louisiana Purchase covered approximately 828,000 square miles.

The United States acquired the territory from France in 1803 for $15 million. The purchase greatly expanded the nation, adding land west of the Mississippi River and east of the Rocky Mountains, although the exact boundaries and ownership of some areas were initially unclear.

President Thomas Jefferson supported the acquisition because control of the Mississippi River and the port of New Orleans was important to western farmers and national commerce. The agreement was negotiated by American diplomats Robert Livingston and James Monroe with French statesman Talleyrand.

The Louisiana Purchase roughly doubled the size of the United States. It included all or parts of fifteen present-day states and the present-day territory of Louisiana, though the modern state boundaries did not yet exist.

The purchase also intensified disputes over Indigenous sovereignty, slavery’s expansion, and the legal limits of presidential power. Jefferson had favored a strict interpretation of the Constitution, yet the Constitution did not expressly describe a land-purchase power.