The purchase price for the Louisiana Purchase was $15 million, an acquisition that nearly doubled the United States in 1803.
The United States agreed to buy the Louisiana territory from France through a treaty signed on April 30, 1803. The payment included $11.25 million in cash and the assumption of claims by American citizens against France worth $3.75 million, producing the commonly cited total of $15 million.
The deal transferred about 828,000 square miles of territory west of the Mississippi River and east of the Rocky Mountains. President Thomas Jefferson supported the purchase, although he worried about whether the Constitution explicitly authorized acquiring new territory. The agreement was not a purchase of the modern state of Louisiana alone; it covered a vast region containing land that later became parts of numerous states.