The International Federation of Association Football, or FIFA, says that a professional game between two teams of 11 players must take place on a field that is between 100 and 130 yards long and 50 and 100 yards wide. So, the total square footage is somewhere between 45,000 and 117,000 square feet.
FIFA says that the best size is between 110 and 120 yards long and 70 to 80 yards wide. This means that the best field is between 69,000 and 86,000 square feet in size. A professional American football field, on the other hand, is 53.3 yards wide and 120 yards long, making it 57,564 square feet in size.