• Photo for Calculate your calorie requirements
    Photo Credit: Shutterstock

Calculate your calorie requirements

By Nikki McDonald

You know you need a certain percentage of proteins, carbs, and fats to reach your fitness goals, but in order to turn those percentages into meaningful portions of chicken, pasta, and cheeses you first need to determine how many calories you need to consume in a day. In other words, before you can begin slicing the pie, you need to know how big it is.

"The number of calories you need each day," says San Francisco-based registered dietician and nutritionist Manuel Villacorta, "is based on your total energy expenditure, which is determined by three things: your resting metabolic rate, lifestyle, and exercise level."

Clear as mud, right? Villacorta helped us break it down.

Resting Metabolic Rate
Your brain, immune system, muscles—every organ in your body—needs energy, or calories, to function. Your resting metabolic rate (RMR), or metabolism, is the amount of energy your body burns just to stay alive.

Whether your scale shows it or not, you burn a lot of energy just by living—your RMR accounts for 60 to 70 percent of your total energy output, says Villacorta. RMR is based on such factors as age, gender, body composition, weight, and even genetics. As you grow older, for example, you decrease muscle mass and your metabolism decreases, which is why you gain weight as you age.

You can measure your RMR by breathing into a machine called an indirect calorimeter, which measures the oxygen that the body consumes and calculates the number of calories your body burns at rest each day. Some gyms offer this service.

One way to get a rough idea of your metabolism, says Villacorta, is to determine your ideal weight and add a zero to the end of it. For example, if you're fit and weigh a healthy 175 pounds, 1,750 would be your metabolism. If you weigh 175 pounds, but are 25 pounds overweight and really should weigh 150 pounds, then you'd use 1,500 as your RMR.

Lifestyle is also key to determining how much energy you burn in a day. Are you sitting at work most of the day? Standing? Working construction? Say your RMR is 1,750 and you sit at a computer all day. In this case, you'd want to add about 20 percent, or an additional 350 calories, to your RMR for a total of 2,100 calories used up each day working and surviving. If you're more active, you'd add between 30 and 50 percent, and if you're super active, like a construction worker, you'd add 60 to 80 percent to your base RMR.

Unless you're a couch potato whose idea of working up a sweat is reaching for the remote, you'll also need to factor in how much energy you burn through exercise to determine your total energy expenditure for a day.

The number of calories you'll burn through working out is impacted by the frequency of your workouts, the intensity of your workouts, and your body weight. You can consult a trainer at your gym to help you determine how much you burn in a workout, or, if you don't have easy access to a trainer you trust, you can also use a heart monitor.

If you choose to use a heart monitor, be sure to buy one that tracks how many calories you burn in a workout, advises Villacorta, as not all of them do. Using the heart monitor, keep track of how many calories you burn per workout—each time you work out—for one week. At the end of the week, add up your total calories and divide by seven days to find out how many calories you burn on average per day as part of your exercise routine.

For example, if you generally exercise on Monday, Wednesday, and Friday, and on those days your heart monitor shows that you burn 500 calories, 600 calories, and 600 calories, respectively, then simply add those numbers up to learn that you burn 1,700 calories per week through exercise. To figure out how many calories you burn on average each day through exercise, just divide by seven days for a total of 243 calories burned daily.

Determining Total Energy Expenditure
To determine your total energy expenditure, you'll need to add the amount of calories you burn in a day by exercising to your RMR (adjusted to account for your lifestyle, of course.)

So, going back over our earlier calculations, if your RMR is 1,750, but you work at a computer all day, you'll add 350 calories (20%), to your RMR for a total of 2,100 calories. You're not done here though. If, through exercise, you burn an additional 243 calories per day, you'll need to add 243 to 2,100 for a total energy expenditure of 2,343 calories.

Slicing the Pie
After you've figured out your total energy expenditure per day, you can begin to determine exactly how many of the calories you take in each day should be composed of proteins, carbs, and fats.

Villacorta offers an example. Say your total energy expenditure for the day (the amount of calories you need) is 2,500 calories, you're 5'8" tall, and you weigh 152 pounds.

If you do a lot of strength training to build muscle, proteins are of prime importance, so you'll want to start by figuring out how many proteins you need (See the related article "Following the Protein Craze" below to determine how much protein you need). Serious weight lifters want to consume one gram of protein for every pound they weigh—the maximum amount of protein you should eat in a day. In this case, you'll need about 152 grams of protein as part of your daily diet.

How many calories is that? Considering that a gram of protein equals four calories, multiplying 152 by 4 shows that 608 of your daily calories—about 24 percent—should come from protein.

You still have 1,900 calories left. If 24 percent of your overall calories are coming from protein, you'll want to divide the remaining 76 percent between carbs and fats. To stay fit and build muscle, 20 percent of those calories should come from fats and 56 percent should come from carbs.

How many grams of carbs does that mean you need? As with protein, you get four calories for every one gram of carbohydrates you consume. For every gram of fat, you get nine calories. You can estimate how many grams of each you need by knowing your percentages. Do the math and you should wind up with 350 grams of carbs. Divide the remaining 500 calories by nine for 55.5 grams of fat.

Your final diet, in this hypothetical case, should include 152 grams of protein, 55.5 grams of fat, and 350 grams of carbs for the day. Now that you know how to work the equation, just run the numbers for yourself, says Villacorta, and you'll soon start seeing results.

Nikki McDonald is a freelance writer and editor based in Minnesota. She has previously worked as the editor in chief of Digital Photography magazine and executive editor of MacAddict magazine, among others.

Manuel Villacorta is a registered dietitian/nutritionist located in San Francisco, California, providing nutrition counseling in weight management and various nutrition-related topics. He can be found on the web at