If you eat a lot of boxed and packaged foods, then learning how to count and calculate calories is a snap because all of the information you need is right there on the label, but if you like to cook or are trying to save money or eat healthier, then you are probably using more whole, fresh or frozen foods, which may not come with a nutrition label. And even if they have a label, you still need to do the math to figure out the calories in a complex dish like broccoli casserole or baked spaghetti. Using some basic math skills and a good source of nutrition information, you can easily learn to count and calculate calories yourself.
Step 1
Locate a source for nutritional information. If all of your chosen foods are pre-packaged, then you should have all the information you need right on the label. If you are using fresh or bulk purchased foods, then you will need a supplemental source of information. There are books, of course, that have this information, but there are also plenty of websites and software programs available that give calorie counts for thousands of common food items. One of the most comprehensive is the USDA nutrient database, which is available to download or search online (see References).
Step 2
Gather the list of ingredients and measures for the food you want to count calories on. If your food choice is something simple like a glass of orange juice, there is only one ingredient, so there is not much to calculate, but if you want to eat a bowl of oatmeal with brown sugar, raisins, and a splash of cream, then you will need to do a little more work. This breakfast meal will serve as an example of how to calculate calories: one cup cooked oatmeal, two tablespoons brown sugar, one quarter cup raisins, one tablespoon heavy cream and an eight ounce glass of whole milk.
Step 3
Find the calorie count for each ingredient in its standard serving size. Look on your package label for this, or look it up in your other source. This example will use values from the USDA nutrient database. These are the standard serving sizes and their associated calories for the items in our ingredient list: one half cup uncooked oatmeal, 133 calories; brown sugar, 836 calories per cup; raisins, 434 calories per cup; heavy cream, 52 calories per tablespoon; whole milk, 149 calories per cup.
Step 4
Translate the standard serving size calories into the calories for the amount you will consume. To do this, you have to convert from one serving size to the other, and then multiply the calories by that same factor. Here is an example: the calories given for brown sugar were for a whole cup, but the oatmeal in the example used only two tablespoons, which is one eighth of a cup, so the calculation is 1/8 x 836 = 104.5 calories. Likewise, the raisin calories for a quarter cup would be 1/4 x 434 = 108.5. For the oatmeal, a half cup uncooked will yield one cup cooked, so the calories stay the same, and for the heavy cream and the milk, the serving sizes are the same as those given in the database, so the calories will be the same.
Step 5
Compute the total calories. The total calories for this breakfast would be oatmeal + brown sugar + raisins + heavy cream + whole milk = 133 + 104.5 + 108.5 + 52 + 149 = 547.
Tips and Warnings
- The hardest part for most people is converting the serving size in the nutrition information source to the serving size they are eating. For example, a bag of potato chips might indicate the calories in a one ounce serving, but you might have no idea how many chips are in one ounce. One trick here is to look at the servings in the whole bag and estimate what portion of the bag you consumed. You might think that you ate about one fourth of the bag, and the whole bag had 10 ounces, so your portion was 10 / 4 = 2.5 ounces.
- If you calculate the total calories for a meal or food item, but then find that you don't eat it all, you will have to do one more calculation. Try to estimate what portion of the whole food you did consume, and then multiply that percentage by the total calories in the food. For example, if you only ate two-thirds of your bowl of oatmeal but drank all your milk, your total calories would be 2/3 x (133 + 104.5 + 108.5 + 52) + 149 = 414.
Things You'll Need
- Calculator
- Menu or ingredient list
- Nutrition information, either from the package label, a book, a website, or a software program
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