How To Calculate BMI

How To Calculate BMI

You don’t need to be a kinesiology graduate to understand the basics behind calculating calories, figuring out your macros, or determining what your Body Mass Index (BMI) is. In fact, being able to use simple formulas and calculations to find out basic information about your body could be very beneficial to your fitness journey and health in general.

What is BMI?

The BMI gives us an approximation of our body composition. While the BMI calculation does not precisely calculate the body fat percentage, Center for Disease Control and Prevention states “BMI is moderately correlated with more direct measures of body fat obtained from skinfold thickness”. The higher the BMI, the less “proportionate” our body should be in terms of weight in comparison to height.

However, the BMI calculation is not flawless and should be only considered as a basic predictor of one’s body composition. One of the issues with the concept of BMI is the fact that a person’s muscle mass is not considered in the calculation and gender or age is not considered either.

Muscle weighs more than fat does and that simple fact could throw the equation off a little. Additionally, women tend to have more body fat than man even when they’re both in the same BMI bracket [1]. Age can also play a role in body fat. All these factors should be considered for more approximate measures of body fat and body composition.

calculate bmi

BMI Calculation & How To Interpret It

The basic formula calculates the person’s weight in kilograms divided by the square of height in meters [2]. Below, I will include both formulas in the metric system, as well as in the imperial system. Based on numerous sources, interpreting the results is fairly straightforward. National Heart, Lung, and Blood Institute estimates the results as follows [3]:

☐ Underweight = less than 18.5

☐ Normal weight = 18.5 – 24.9

☐ Overweight = 25 – 29.9

☐ Obesity = BMI of 30 or greater

Don’t worry, though, like I previously mentioned, the results should be interpreted as estimates rather than an exact projection of your body composition.

Based on the Centers for Disease Control and Prevention, the formula for calculating the BMI (in kilograms) is [4]:

☐ Weight (kg) / [height (m)]2 . For example, if a person weighs 80kg and is 85m tall, the equation would be: 80 / (1.85)2, and the BMI would be 23.37.

☐ The result of 23 would mean that the person falls in the bracket of a normal weight.

The formula for calculating the BMI (in pounds) is:

☐ Weight (lb) / [height (in)]2x 703. For example, if a person weighs 200 lbs, and is 5’10” (70 inches) tall, the equation would be: 200 / (70)2 x 703, and the BMI would be 69.

☐ The result of 69 would indicate that the person falls into the bracket of being a little bit overweight.

As you can see, the equation is very easy to put together and only takes a couple of minutes to figure out your BMI, whether you use the metric or the imperial unit system.

how to intepret bmi

BMI Implications

One of the implications of calculating your BMI is to basically determine a ballpark of your current body composition and to get a fairly simple estimate of the fat content related to your height and weight. BMI is understandably not the most accurate measure of your body fat content, however, it is useful to see the approximate measures provided by this calculation.

Note that for more accurate measures of your body fat you could book a DEXA (Dual Energy X-ray Absorptiometry) scan or do a Hydrostatic Weighting that would measure your body composition much more precisely than a BMI calculation, however, these tests can be rather costly as well as challenging to find. For someone wanting to know a little bit more about their own body, a BMI calculation should serve the purpose just fine, and it’s completely free and fun to figure out stuff about your body on your own, give it a try!

implications of bmi

Take Home Message

Even though the BMI calculation will only give you an assessment of your body composition, it is a great place to start if you’re just getting into fitness, or if you want to find out more about your body and health in general. You can calculate your BMI to see where you stand, and even if the result is not what you would like it to be, don’t worry!

It is not a flawless estimation, and as previously mentioned, many factors are not included in the calculation to make it more precise and determining. Take these results as a basic measurement of your body and a starting point. Set your goals where you want to get and work towards those goals and maybe once in a while, come back to the formula and check your BMI to see if you’re improving with the results. Regardless of the answer of the equation, keep your head up, put in the work at the gym and in the kitchen, and have fun in the process!

[1] Why Is BMI Important?.

[2] About Adult BMI.

[3] National Heart, Lung, and Blood Institute. Calculate Your BMI.

[4] About Adult BMI.

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Vojtech Velecky

Vojtech Velecky

Writer and expert