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Basal Metabolic Rate Calculation

The basal metabolic rate calculation takes into account many different variables. There are different methods used for BMR calculation with the most common calculation being the Harris-Benedict formula. This formula uses height, weight, age and sex to determine your basal metabolic rate. The results of the BMR calculation using these variables are an estimate, but will be fairly accurate for most people.

Click here to use the free interactive BMR calculator on this site.

Basal Metabolic Rate Calculation Explanation

calculator

You may be wondering why and how the variables are used in the basal metabolic rate calculation. 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 metaoblic 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.

Basal Metabolic Rate Calculation Harris-Benedict Formula

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.

You can also use this google gadget to convert from lb to kg and inches to cm. Just type in your weight followed by lb (or pounds) and then type in the measure you want to convert to (kg). For your height, you can type in feet and inches to convert to cm. Example, type in 5 ft 6 in and in the second box type in cm to convert to centimeters.

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 is you want to ensure you are consuming enough calories for your BMR as well as you level of exercises. 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

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