An American Football field is 100 yards long, plus 2 endzones of 10 yards each. Making it 120 yards long total from goal post to goal post. It is 53 1/3 yard wide. In other words it is 360 feet by 160 feet.

The hashmarks which the ball must be placed between are 70 feet, 9 inches from their nearest sideline. Which means there is 16 feet, 6 inches between the hashmarks. Again in other words that is 5 1/2 yards between the hashmarks.

Most football fields are not flat. There is a slight curve to the field's playing surface with the highest point down the center of the field and dropping away slightly as you proceed toward the sidelines.

But that is just a basic professional American Football field. There is Canadian Football, Rugby, Soccer, and various forms of American High School Football that all have different sized fields.