What number of calories should a 13 year old eat in each day?

It depends: Caloric intake requirements in teenagers depends on how active they are, what size they are at the time (ie underweight, overweight, normal), and how tall they are. In general teenage girls need 1600-2200 calories per day. More important is to make sure the food is of high quality including 6-8 servings of fruits and vegetables, whole grains, lean protein, and calcium containing food.