An American football field is 100 yards from goal line to goal line.
That measurement describes the field of play, excluding the two end zones. Each end zone is 10 yards deep, so the complete playing surface from end line to end line measures 120 yards. This is why both 100 yards and 120 yards can appear in football discussions, but the question’s goal-line-to-goal-line wording specifically calls for 100 yards.
The field is 53⅓ yards wide, or 160 feet. Yard lines run across the field at five-yard intervals, while smaller hash marks help determine where many plays begin. The midpoint is the 50-yard line, and each team’s territory extends 50 yards from midfield to its own goal line.
The standardized 100-yard field also makes statistics easier to compare across games and eras. A 90-yard answer confuses the field with neither the regulation playing area nor the distance between the goal lines; it is simply not the standard NFL measurement.