BMR Calculation

Basal Metabolic Rate

If you are curious about the math behind this BMR calculation, then be sure to read on. If you are looking for the online calculator, click here.

With this article you will learn more about your basal metabolic rate and how it's calculated.

The basal metabolic rate calculation takes into account many different variables.

There are different methods used for the calculation with the most common being the Harris-Benedict formula. 

This formula uses height, weight, age and gender to determine your basal metabolic rate. 

The results of the Basal Metabolic Rate calculation using these variables are an estimate, but will be fairly accurate for most people.

No one formula will be exact as there are other factors, such as family traits and frame size that are not taken into account.

Therefore all of the various calculators will be an approximation of your BMR.

BMR Calculation Explained

There are several variables that are used in the BMR calculation. These include age, gender, weight and height. These factors are used to determine your resting BMR.

Additionally the activity level is used to determine your total daily caloric needs. You may be wondering why and how these variables are used in the BMR calculator.  

Well, age plays a role in your metabolic rate.  As we age, our metabolism slows down.

I know this doesn't seem fair to those of us over 40, but it's true. Gender also plays a role in the calculation.  

Why?  Well men tend to have more lean muscle and the more lean muscle you have the higher your basal metabolic rate.

Lastly, body surface is needed to determine your BMR calculation.  This is why both weight and height are used. The more body surface you have, the more calories you burn through your basal metabolic rate.

However, because lean body mass is not a variable in the Harris Benedict formula, it may be inaccurate for those that are extremely muscular as it may underestimate caloric needs.  This is because muscles are more metabolically demanding than fat. 

It may also be inaccurate for people with an extremely high percentage of body fat, overestimating their caloric needs as your body uses fewer calories to sustain the fat.

Harris-Benedict Formula

As stated above, this BMR calculator is using the Harris-Benedict formula to determine the results. Note that this formula uses kilograms for weight and centimeters for height. Below this formula you will see the conversion factors to use for pounds and inches.

Men:  66 + (13.7 x weight) + (5 x height) - (6.8 x age in years)

Women: 655 + (9.6 x weight) + (1.8 x height) - (4.7 x age in years)

Metric to Imperial conversion
1 inch = 2.54 cm

Example, if you are 5’3” (or 63”), then you height in cm equals 63 inches x 2.54 cm = 160 cm

1 pound = .45 kg (1 kg = 2.2 pounds so 1 pound divided by 2.2 kg equals .45)

Example, if you weight 160 pounds, then your weight in kg equals 160 lbs x .45 kg = 72 kg

So, if you are a 40 year old female weighing 150 pounds at 5’3” (or 63 inches), your calculation would be;

655 + (9.6 x [150 lbs x .45 kg]) + (1.8 x [63 inches x 2.54 cm]) – (4.7 x 40)

655 + (9.6 x 68 kg) + (1.8 x 160 cm) – (188)

655 + 653 + 288 – 188 = 1408 calories/day

The Activity Factor

A weight loss calculator will use the results of your basal metabolic rate calculation and then factor in an activity level.  This will give you the amount of calories you burn based on the BMR as well as your exercises.

The reason you need to understand the activity factor for this BMR calculator, is you want to ensure you are consuming enough calories for your BMR as well as your level of exercise.  By factoring in the activity level in a weight loss calculator you will get the proper daily calorie intake needs to sustain and/or lose weight.  

Below is what is used to factor in the activity level.

Exercise/Activity multiplier

Activity Level

Factor

Description 
Sedentary BMR x 1.2 no or little exercise
Lightly active BMR x 1.375 light exercise 1 - 3 days/week
Moderately active BMR x 1.55 mod. exercise/sports 3 - 5 days/week
Very active BMR x 1.725 hard exercise/sports 6 - 7 days/week
Extremely active BMR x 1.9 hard daily exercise/sports plus physical job or exercise 2x a day

Example:

If your basal metabolic rate is 1408, then based on your activity level, your daily calorie needs to maintain your weight would be as follows;
  • Sedentary = 1408 x 1.2 = 1690
  • Lightly active = 1408 x 1.375 = 1936
  • Moderately active = 1408 x 1.55 = 2182
  • Very active = 1408 x 1.725 = 2429
  • Extremely active = 1408 x 1.9 = 2675

Now that you understand the BMR Calculation, use the online calculator to find your Basal Metabolic Rate.


Additional Articles

BMI Calculation
Find out how to calculate your Body Mass Index by reading this article. The BMI is used as a guide to see if you have medical risks due to your weight.

Target Heart Rate Calculator
Here is another free online calculator you can use to ensure you are working out within your target heart rate zone.

Metabolism Boosters
Give your BMR a boost with these metabolism boosting tips. Find ways to rev up your metabolism will help you burn more calories in a day.