How do you determine how many calories are in a food product?

There are two answers. If you are making the food yourself, you go on a site like this and find out the calorie count for the individual ingredients, add them up, and then divide the number of servings into that number to get the single serving calorie count.

For instance, I just made peanut butter cookies and wondered how many calories in each cookie. There are five main caloric ingredients--Sugar, 775 calories per cup; Flour, 1000 calories per 2 1/2 cup; Peanut Butter, 1520 c. per cup; Butter, 1600 c. per cup; and Eggs, 150 c. for 2 large eggs. The total of all that is 5045 calories. I divided that by 73, the number of cookies the recipe made, to equal about 69 calories per cookie.

It's pretty hard to find out the calorie count in store-bought food without the panel of nutritional information on the side of the box. You could call the manufacturer and they'd tell you. A lot of restaurants are posting the caloric content of their foods on menus.