The current United States flag has 13 stripes, representing the original thirteen colonies that declared independence from Great Britain.
The stripes alternate red and white and remain fixed at thirteen, even as the number of states has grown. The blue canton contains stars for the states, so the flag now has 50 stars.
Congress originally authorized a flag with thirteen stars and thirteen stripes in 1777. In 1795, two additional stripes were added for Vermont and Kentucky, creating a 15-stripe flag. The 1818 Flag Act restored the number of stripes to thirteen and established that future states would be represented by new stars.
A common mix-up is assuming that the stripes represent the states. They represent the original colonies; the stars represent the current states. The 50-star design became official on July 4, 1960, after Hawaii joined the Union.