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What is BMI and How to Calculate it?

Normally, we judge the fitness of a person by his weight. If we hear that someone is 80 or 90 kilograms or even more, it is an instinctive reaction to raise eyebrows and imagine a plus size person with a double chin, a protruding belly and a huge appetite for sure. The fact that the person can actually be absolutely fit in spite of his weight is surely unfathomable.

But in reality, weight alone cannot be the criteria to judge if a person is overweight or underweight. Apart from other factors like bone weight, body metabolism rate etc. what is one of the more easy to understand factor that plays an important role in judging the fitness of an individual is his height and therefore, most experts rely on measuring the Body Mass Index (BMI) rather than just the weight to analyse the health of an individual.

What is BMI?

BMI is the gross estimate of the fat present in your body and it is a standardisation of the varied height and weight that people might have. The healthy weight range that you see in many diet charts is based on the BMI and if you know your weight and height, you can easily calculate your body mass index to know if you fit in the normal weight range or not.

Two people with same weight may have different heights and therefore their BMI will be different from each other.

According to the BMI chart,
BMI                            Fitness Level

18.5 or less                      Underweight

18.5-24.9                          Normal

25.0-29.9                          Overweight

30.0-39.9                         Obese

40.0 or more                  Extremely Obese

Doctors and nutritionist like the BMI because it is a shorthand that helps them describe the fitness of a person easily. It also enables them to use a single number and a range to describe the fitness quotient of a person whether a male or a female.

How to Calculate BMI

To calculate your BMI,
• Find your weight in kilograms
• Find your height in metres and square it.
• Divide the weight by the height squared which give you the BMI number
• You can them check the number with the chart to figure out if you are considered within normal fitness range or not.

For instance, if your weight is 55 Kg and height is 1.5 m your BMI will be,
1.5 x 1.5 = 2.25
55/ 2.25 = 24.44
which is within the normal BMI range.

Ideally for Indians, doctors consider 23 BMI to be the best.

BMI is not Definite Indication of Fitness

Although calculating BMI is a great way to know if you are overweight or underweight or visibly obese, it is not a definitive measure to assuredly say that you are fat or not. It is because the muscular weight of the body is not being considered while making the estimate.

A body builder who has low body fat may still come under the overweight range because of his muscular weight. On the other hand not all who fall under the range of normal BMI may actually be healthy considering their lack of exercise, low stamina, high cholesterol level etc.
BMI is also not applicable for children, pregnant women, older people and those who have serious health conditions.

For the purpose of knowing where you stand in the ideal world and how much you have to push yourself through exercise to become fitter, BMI is a good indicator. But do know that your body is made of many more things than fat and it is all these things in combinations that decide your fitness level.

Image Credit xJasonRogersX via cc/Flickr

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