The number of calories in a bag of popcorn varies widely depending on the type, brand, preparation method, and size of the bag:

• A small bag of plain, air-popped popcorn typically contains about 110 calories (around 31 grams)

• Microwave popcorn bags generally contain between about 400 to 600 calories per bag, depending on added butter, oil, and flavorings. For example, a typical microwave popcorn bag may have around 535 calories

• Some medium-sized movie theater popcorn bags can contain over 700 calories, with one example listing 762 calories for a 160g bag

• Calorie estimates can also be calculated by volume: about 30-35 calories per cup of popped popcorn, with a full bag yielding 10-11 cups, totaling roughly 330-350 calories per bag for plain popcorn

• Buttered or flavored popcorn varieties have higher calorie counts due to added fats and sugars, with caramel popcorn around 120 calories per cup

In summary, a typical bag of plain microwave popcorn ranges from about 300 to 600 calories, while movie theater or buttered varieties can be significantly higher, sometimes exceeding 700 calories or more per bag. Always check the specific product label for the most accurate calorie information.