How to Convert Macronutrients to Calories?


New diets can be confusing.  Depending on which diet you choose, you might be asked to count calories.  Counting calories takes a bit of practice and learning how to convert macronutrients to calories is what calorie counting is all about.

As luck would have it, learning to add calories is a breeze.

Macronutrients, or “macros”, consist of protein, carbohydrates and fat.  Protein and carbs contain exactly four calories p/ gram and fat contains nine calories p/ gram.

Let’s say you bought a box of Kraft Macaroni & Cheese.  It was the only thing that looked good in the kitchen so you fixed it as instructed on the side box instructions and ate half a box.  How many calories did you consume?

If you look at the label, you could obviously do the math on this one in an easier manner.  Since the label specifies the serving size is 1/4 of the package, you would just multiply by two and have your calories.  But..for the sake of learning how to do these calculations on our own (because it won’t always be this easy), let’s just pretend that we only know the amount of protein, carbs and fat in this box.

The “per serving” amounts are as follows:

  • Protein: 13 grams
  • Carbohydrates: 50 grams
  • Fat: 4.5 grams

How to Calculate

Remembering that protein has 4 calories p/ gram, carbs have 4 calories p/ gram and fat has 9 calories p/ gram, we calculate our cheesy lunch in this manner:

  • Protein:  13 x 4 = 52 calories p/ serving.
  • Carbohydrates: 50 x 4 = 200 p/ serving.
  • Fat: 4.5 x 9 = 40.5 calories p/ serving.

With a serving constituting 1/4 of the box, that’s 290.5  (52 + 200 + 40.5) calories p/ serving. If the box had 8 servings p/ container, we would multiply by half of that (four) to get the number we need.  In this case, we know the serving size to be 1/4 of the box, so we simply multiply 290.5 x 2 for a grand total of 581 calories consumed.

Macros and Calories

Let’s take our example one step further and pretend that you’re on a 1800 calorie a day diet.  Maybe 40% is supposed to be protein, 40% carbohydrates and 20% fat?

We would track and record our macros (protein, carbs and fat) to calculate appropriately. First we need to know how many macros we’re allowed every day?

AT 1800 calories, we need 40% to be protein.  1800 x 40% = 720.  Since protein is 4 calories p/ gram, we divide 720/4, which equals 180.  That’s how much daily protein is needed.  Carbs are the same at 40% and the same calories p/ gram.  Fat is 9 calories p/ gram so the equation is as follows:  1800 x 20% = 360 / 9 = 40 grams of fat a day needed.

Half a box of Mac & Cheese supplied almost exactly 1/3 of the daily calories needed.

The lesson here isn’t only in calculating calories but in spacing meals out and not eating too much at once.  It can sometimes be easy to hit the daily caloric goal before 5pm and that’s setting oneself up for failure, so be smart in how you allocate calories.

Counting calories can be an eye-opening experience into how much a person is eating on average but now that you know how to convert macros to calories, losing those extra pounds is just a matter of commitment.


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