Body Mass Index (BMI) and its Calculation

What is BMI?

Body mass index (BMI) is a measure of body fat based on your weight in relation to your height, and applies to most adult men and women aged 20 and over. For children aged 2 and over, BMI percentile is the best assessment of body fat.


BMI = body weight (in kgs)/[height (meters)] squared

  1. Multiply your height in meters (m) by itself
  2. Divide your weight in kilograms (kg) by your step 1 result


For an adult with height of 180 cm and weight of 75 kg. Our first step needs to be to convert the height into meters (British spelling: metres). As there are 100cm in a meter, we divide our figure by 100. This gives us 1.8m.

Let’s plug those figures into our formula:

BMI = 75 ÷ (1.8 × 1.8)

BMI = 75 ÷ 3.24

This gives us a BMI figure of 23.15.


According to the World Health Organization (WHO), BMI is classified into four major categories:

Underweight: 15 – 19.9

Normal: 20 – 24.9

Overweight: 25 – 29.9

Obese: Greater than or equal to 30

For example, an individual with a BMI in the range of 15 – 19.9 would be considered as underweight and normal if the BMI is in the range of 20 – 24.9.

However, obesity was further classified into three major classes with values as follows:

Class I obesity: 30 – 34.9

Class II: 35 – 39.9

Class III obesity: greater than or equal to 40

According to a 2015 study published in the Journal Nutrition Today, there has been an increase in BMI in the general population over the past several decades. As the mortality rates increase with increasing degrees of overweight and obesity, it is important to keep a close tab on your BMI & weight.

The higher the BMI, the higher the is risk of various metabolic diseases such as:

-High cholesterol

-High blood pressure

-Type 2 diabetes

-Heart disease

-Metabolic syndrome

-Coronary artery disease



-Breathing problems

-Gallbladder disease


-Polycystic Ovarian Syndrome (PCOS)


BMI is considered as a poor indicator of percent of body fat, however is is commonly used as a risk factor for various health problems.