How to calculate calories from a nutrition label?

Serving size is imp!: Nutrition labels label the calories alone but it's the serving size where things get tricky. For example, if the serving size says 1 cookie and the calories say 120 calories. That's not a good idea however if the 50 berries is about 50 calories that's 1 calorie per berry. But food is much more complicated than that. Take nuta. They are high in calories but very nutritious. Just eat less...

Multiply it out: Calories per serving are listed on each nutrition label. But you really want to know how many calories are in the whole box/bag/can. Multiply the number of servings in the container times the calories per serving to get the total calories. The serving size on the container usually is nowhere close to what people actually eat.

4,4,9: its four calories per gram of protein plus 4 calories per gram of carbs and add 9 calories per gram of fat for the total number of calories