Calculating how many calories you need to eat to reach your weight loss and fitness goals 

How many calories should you eat to burn fat or build muscle?

These are loaded questions...and the answer is...it depends. It depends on what your goals are and where you are right now. If you want to build muscle your calorie needs will be different than if you want to burn fat. If you are 6’-2” tall and generally active your caloric needs will be different from the guy who is a 5’-8” (reforming) couch potato.

Rather than being able to give you a pat answer, you are going to need to assess your current situation, understand a couple key concepts and then do some math.

We’ve already discussed how to measure body fat which is a critical component to our calculations. Next let’s cover some basic terminology you will need to understand before you can finish the math.

Basal Metabolic Rate or BMR

Your BMR is defined as the number of calories your body consumes at rest. In other words what it takes to keep you breathing, your heart beating, and the basic functions of all your organs to process food, eliminate waste, etc. This is the base line...you need to eat this number of calories just to stay alive.

Lean Body Mass or LBM

Lean body mass is how much your bones, muscles, and organs weigh...how much you weigh without body fat. To determine your LBM you must know how much you weigh and how much body fat you carry. From there it is a simple equation:
Total weight – weight of body fat = Lean Body Mass

Body Mass Index or BMI

BMI is a term that is thrown around a lot and you should understand what it means and why it is, and isn’t, useful.

BMI is standard number that many doctors use to determine if you are in a healthy weight range or if you are under or overweight. BMI charts are available online, at most gyms, and probably at your doctor’s office. You can determine your BMI without a chart with this math equation:
(Total bodyweight in pounds x 703) / (your height in inches 2)

A “normal” BMI range is 18.5-25. Higher numbers represent overweight, lower numbers represent being underweight.

Like any other system based on averages or simple equations, using the BMI to assess your health has its limitations. For one, it does not include your physical condition or your basic build. Because muscle weighs more than fat, if you are more muscular either because of genetics or from working out, your body will weigh more and on the chart you may appear to be overweight when you actually have very little fat.

Calculating Your BMR using LBM

1. A rough estimate of your BMR can be reached by multiplying your LBM by 11.

2. A more precise formula is called the “Katch-McArdle” formula which is
BMR=370 + (21.6 x LBM in kilograms)

Don’t know kilograms? Take your LBM in pounds and divide it by 2.2 to get LBM in kilograms.

Calculating Your BMR without LBM

It is possible to estimate your BMR without knowing your LBM, but it won’t be as exact...just like the BMI chart it will be based on averages and will therefore will indicate you need more calories than you do if you are overly fat and will provide a low estimated caloric need if you are more muscular.

This formula is called “Harris-Benedict Equation,” to use it you need to know your weight in kilograms, height in centimeters and your age in years.

Converting weight: divide weight in pounds by 2.2 to get weight in kilograms.

Converting height: multiply your height in inches by 2.54 to get your height in centimeters.

Men
BMR=66 + (13.75 x weight) + (5 x height) – (6.8 x age)

Women
BMR= 655 + (9.6 x weight) + (1.8 x height) = (4.7 x age)

The Harris-Benedict Equation was originally created in 1919 and a more recent equation established in 1990 by Mifflin-St Jeor is:

Men
BMR= 5 + (10 x weight) +(6.25 x height) – (4.92 x age)

Women
BMR= (10 x weight) + (6.25 x height) – (4.92 x age) -161

Now that you have calculated your BMR, how many calories your body uses at rest, you can now determine how many calories you need to consume in order to burn fat or build muscle.