Body Mass Index - Calculate Yours!

Body Mass Index (BMI) is a simple index of weight-for-height that is commonly used to classify adults as underweight, overweight and obese. BMI is defined as the weight in kilograms divided by the square of the height in meters (kg/m²). BMI has become a very common method to assess adults for their nutrition status. The weighing machines installed in every nook and corner of public places are also programmed to assess the weight as well as the BMI of an individual. BMI is also called as Quetlet Index.

BMI =    Weight (kgs)
            Height²(m)

The International Classification of adult underweight, overweight and obesity according to BMI is:

	Principal cut-off points	Additional cut-off points
Underweight	<18.50	<18.50
Severe thinness	<16.00	<16.00
Moderate thinness	16.00 - 16.99	16.00 - 16.99
Mild thinness	17.00 - 18.49	17.00 - 18.49
Normal range	18.50 - 24.99	18.50 - 22.99
		23.00 - 24.99
Overweight	≥25.00	≥25.00
Pre-obese	25.00 - 29.99	25.00 - 27.49
		27.50 - 29.99
Obese	≥30.00	≥30.00
Obese class I	30.00 - 34.99	30.00 - 32.49
		32.50 - 34.99
Obese class II	35.00 - 39.99	35.00 - 37.49
		37.50 - 39.99
Obese class III	≥40.00	≥40.00

                 Source: Adapted from WHO, 1995, WHO, 2000 and WHO 2004.

A frequent use of the BMI is to assess how much an individual's body weight departs from what is normal or desirable for a person of his or her height. The weight excess or deficiency may, in part, be accounted for by body fat (adipose tissue) although other factors such as muscularity also affect BMI significantly. For adults, a healthy body weight is defined as a BMI of 18.5 to 24.9 kg/m². Those whose body weight is in this range have the lowest health risks. Those with weights above or below this have higher risks of illness and early death. Body mass index of less than 18.5 kg/m² is considered as underweight. Overweight is defined as a BMI of 25 to 29.9 kg/m². Obese is classified as a BMI of 30kg/m² or greater. A BMI of 40 or over is classified as extreme or morbid obesity.

Example to calculate BMI:

What is the BMI of an adult man having a height of 1.62 m and weight 65kg?

We know the formula to calculate BMI is Weight(kgs)/(Height)²(m)

So, BMI of this adult man is 65/ (1.62)² = 24.8 kg/m²

For children over the age of 2 years also healthy weight can be assessed their by BMI, but the cut offs are defined using growth charts with percentiles. A healthy BMI for this age group is one that falls from the 5th to less than the 85th percentile. A child is considered overweight when his or her BMI is greater than or equal to the 85th percentile but less than the 95th percentile and obese when BMI falls at or above the 95th percentile. Underweight children have a BMI of less than the 5th percentile. Following charts will make it easier to understand.

Here is an example to assess the BMI among children:

BMI is not a perfect tool for evaluating the health risk associated with obesity. Someone with a BMI in the overweight range who consumes a healthy diet and exercises regularly may be fit than someone with a BMI in the healthy range who is sedentary and eats a poor diet. It is also possible to have a high BMI but not have excess body fat. E.g.: A weight lifter or an athlete may have a BMI which falls on an obese category. This is because of the muscle mass. But he/she cannot be considered as an obese.

Do not forget to calculate your BMI on our blog. Find the tool on the right column. :) 

Post by Divya Konamme