The official length of an NFL football game is the same every single time two teams take to field. NFL pre-season, regular season, and postseason games are all officially 60 minutes long. Each game is broken into four quarters that are each exactly 15 minutes long. However, the actual length of time that an NFL game is played varies considerably and is never anywhere close to being just an hour long.
Halftime and Injuries
Except for special occasions, such as the Super Bowl, each NFL game has a halftime between the second and third quarters that last 12 minutes. In addition, there is also a mandatory two-minute break between quarters. NFL game time can also be extended in the event of an injury. Most injured players are required to be removed from the field in a timely fashion but in cases where the player may be seriously injured, the player's health takes precedence over regulations regarding a timely exit. Assuming there is no injury stoppage, no timeouts are called, and no stoppage for a penalty review, the least amount of time an NFL game could possibly last would be 76 minutes.
The average NFL game lasts around three hours. The primary reason why a 76-minute game is routinely stretched to at least three hours has to do with television. There are no hard and fast rules or regulations regarding the number of commercials that are allowed to air during an NFL game. Generally speaking, a commercial can be expected whenever possession changes, whenever a team calls a timeout, whenever a player is injured, and following each time either team scores.
If at the end of the regulation period the two teams are still tied, the game goes into overtime. During the regular season the longest that overtime can last is just one extra 15-minute period. During the postseason, overtime must last until one team scores. The longest game in NFL history took place between the Miami Dolphins and Kansas City Chiefs on Christmas Day, 1971. Disregarding the amount of time given over to commercials, the official time of this game was 82 minutes and 40 seconds, a full 22 minutes and 40 seconds longer than a regulation game.