What two numbers defined the flag flying over Fort McHenry in 1814 and inspiring the U.S. anthem?

The flag flying over Fort McHenry in 1814 had 15 stars and 15 stripes.

The large flag was made by Mary Young Pickersgill and workers in Baltimore. Its 15 stars represented the 15 states then in the Union, while its 15 stripes reflected a short-lived design change that added stripes for Vermont and Kentucky, admitted in 1791 and 1792. The flag measured about 30 by 42 feet, making it visible from a considerable distance.

Francis Scott Key saw the flag after the British bombardment of Fort McHenry during the Battle of Baltimore on September 13–14, 1814. The sight inspired his poem, later known as “The Star-Spangled Banner.” The original flag is preserved at the Smithsonian’s National Museum of American History.

The 15-stripe design did not last. The Flag Act of 1818 restored the number of stripes to 13, while keeping one star for each state. That arrangement created the enduring distinction between 13 stripes and a changing number of stars.