Calculations: Part 1

I am a sucker for those online calorie calculators. Every time I come across a site with one, I use it. I don't know if I am looking for confirmation that I am using the right calorie goals or if I'm just a numbers nerd.

In any case, due to the fact that I lose weight by tracking calories, the right calorie intake numbers are important to me. I try to get as accurate a calculation as possible.

To find my daily calorie intake number I can go the short way and use an online calculator (I have some links at the bottom of my "Calculations: Part 3" post) or I can do it the long way:

Step One: Calculate my BMR/RMR.
Step Two: Multiply that number by an activity multiplier to get my Maintenance Calories.
Step Three: Subtract a deficit from my Maintenance Calories to get my Daily Calorie Goal.
Step Four: Eat, exercise and stay as close to my Calorie Goal as possible!

This post will cover Step One.

What is the BMR and RMR?
BMR stands for Basic Metabolic Rate. RMR is my Resting Metabolic Rate.

Basically, my BMR or RMR estimates the amount of calories my body will burn while at rest. If I were to lie in bed all day (no getting up, no moving around...) I would burn a certain number of calories. That number is represented by my BMR/RMR.
The chart below will give you an estimated breakdown of my daily caloric burn:

60-70% - Basic bodily functions (...breathing, temperature regulation, etc.) as represented by my BMR or RMR.
15-30% - All physical activity (walking, running, cooking dinner, chewing gum, tapping my toes...anything other than lying in bed all day.)
10% - Thermic effect of food. (Calories burned through the digestion, asborption and storage of food.)

What is the difference between the two terms BMR/RMR?
These terms are often used interchangeably and the difference between the two is relatively minor.
The difference basically comes from the fact that each rate is clinically measured under two different types of conditions. To get a subject's BMR, he or she must be in a fasted state (so that digestion calories do not play a part in the calculation) and the subject must be in a state of complete rest and in dark, quiet surroundings. It basically just tests how much you burn through regular biological functions.

The test for a person's RMR is not as strict. The subject must be resting, but the calculations can include a some physical disturbance and possibly some digestion. This goes above and beyond BMR testing and includes any additional minor activity that occurs during a rested state.

In any case, we really don't have to worry about any that and we can simply find our estimated BMR or RMR by using an online calculator or by using the equations I will provide below.

What type of BMR/RMR forumlas are available?
Currently there are two popular math formulas to use in order to figure out a person's BMR or RMR. These two formulas are the Harris Benedict Equation and the Mifflin-St.Jeor Equation.
(Note: There is also a way to determine your caloric intake number by lean body mass called the Katch-McArdle formula. However, most people - including myself - do not know their lean body mass, so I won't talk about that method.)

I don't like math. Where are some good online BMR/RMR calculators?
The links below will bring you to two online BMR/RMR calculators:

BMR Calculator (uses the Harris-Benedict Equation)
My Fitness Pal (uses the Mifflin-St.Jeor Equation)

Which do I personally use and why?
I currently use the Mifflin-St.Jeor formula.

While the Harris-Benedict formula is more popular, it has been tested and reported to be slightly more inaccurate than the Mifflin formula. The Harris-Benedict numbers tend to be slightly overestimated (meaning you might be eating more than you should!)

However, some people have great success using Harris-Benedict and many of the popular dieting sites use that formula for their calorie calculations, so it really is up to you to test the numbers and figure out which works best for you.

Just a quick note....it appears that many times a site will use the Mifflin-St.Jeor equation and call the result your "RMR" and then use the Harris-Benedict equation to get a person's "BMR."
Other sites may use both formulas and call both results your "BMR". Don't let that confuse you. They are really talking about the same thing and the most important thing is the number you get from using either formula.

I like math! How do I calculated my BMR/RMR on my own?
First, you need to convert your weight and height into kilograms and centimeters.

This is done by:

Dividing your weight (in pounds) by 2.2.
Multiply your height (in inches) by 2.54.

Example:

A 33-year-old female. You weigh 134 and I am 5'1" (or 61 inches).
134lbs. divided by 2.2 = 60.9 kilograms
61 inches multiplied by 2.54 = 154.9 centimeters

Now, you take those numbers and plug them into one or both of the formulas below.

-------------------------------
* Mifflin-St Jeor Equation *

Men: RMR = (9.99 X weight) + (6.25 X height) – (4.92 X age) + 5
Women: RMR = (9.99 X weight) + (6.25 X height) – (4.92 X age) – 161

Example:
A 33-year-old female. You weigh 134 and I am 5'1" (or 61 inches).
134lbs. divided by 2.2 = 60.9 kilograms
61 inches multiplied by 2.54 = 154.9 centimeters

(9.99 X 60.9) + (6.25 X 154.9) - (4.92 X 33) - 161 =
608.39 + 968.13 - 162.36 - 161 =
1253.16

My BMR/RMR = 1253
So, according to the Mifflin-St.Jeor forumla, these are how many calories you would burn just by lying in bed all day long.

-------------------------------
*Harris-Benedict Formula*

Men
66.5 + (13.75 X weight in kg) + (5.003 X height in cm) - (6.775 X age in years)
Women
655.1 + (9.563 X weight in kg) + (1.85 X height in cm) - (4.676 X age in years)

Example:
A 33-year-old female. You weigh 134 and I am 5'1" (or 61 inches).
134lbs. divided by 2.2 = 60.9 kilograms
61 inches multiplied by 2.54 = 154.9 centimeters

655.1 + (9.563 X 60.9) + (1.85 X 154.9) - (4.676 X 33) =
655.1 + 582.39 + 286.57 - 154.31 =
1369.75

My BMR/RMR = 1370
According to the Harris-Benedict formula, these are how many calories you would burn just by lying in bed all day long.

-------------------------------
Results:

Mifflin-St.Jeor = 1253
Harris Benedict = 1370

Two different equations...two different results.
It's up to each person as to which formula they want to use.

Okay I used the calculator (or did the math.) What happens now?
I now have my BMR/RMR.
Remember this number only accounts for some of the calories we burn each day (about 60-70%). We need to find an estimate of all the calories our bodies burn each day.
This means you have to add youractivity calories, too. That is the only way you can get the best estimate of the total number of calories your body needs every day.

I will explain this next step in the post called "Calculations: Part 2". This is where I calculate in activity levels to find Maintenance Calories.

Note: Remember, there are online calculators to do all of this for us, but some people like to see where the numbers come from, which is why I am explaining it all here.