American college and professional football games are played with a game clock of 60 minutes. Each half of a competition consists of two 15-minute quarters. Timeouts and other clock stoppages prolong the length of NFL games to an average of about three hours and 12 minutes from start to finish.
The intermission between the first and second and third and fourth quarters is two minutes, while halftime is 12 minutes. Team are granted three timeouts per half with each lasting for one minute and 50 seconds. When consecutive team timeouts are taken, the second is reduced to 40 seconds.
The game clock stops momentarily in the event of an incomplete pass or when the ball carrier runs out of bounds. A separate 40-second play clock resets at the end of each play; the offensive team must snap the ball before it expires to avoid penalty. The clock also stops at each change of possession, resuming when the ball is snapped.