What is BMI and How to Calculate Your BMI

Body Mass Index (BMI) is a widely used metric to give a general indication of a person’s body fat based on their weight and height. It is a simple, non-invasive, and relatively inexpensive tool to screen for potential weight-related health issues. In this blog post, we will cover the basics of BMI, how it is calculated, its limitations, and what you can do to maintain a healthy BMI.

The History of BMI

The concept of BMI dates back to the 19th century when Belgian mathematician and sociologist Adolphe Quetelet developed the Quetelet Index. This index was designed as a means to study human growth and development. Later, in the 1970s, the term “Body Mass Index” was coined by American scientist Ancel Keys, who demonstrated the usefulness of the index in assessing population health.

How to Calculate BMI

BMI is calculated using a person’s weight (in kilograms) divided by the square of their height (in meters). The formula for calculating BMI is as follows:

BMI = weight (kg) / [height (m)]²

For those using pounds and inches, the formula is:

BMI = weight (lbs) / [height (in)]² x 703

BMI Calculator

Once you have calculated your BMI, you can refer to the following classification to understand what it means:


  • Underweight: BMI < 18.5
  • Normal weight: BMI 18.5 – 24.9
  • Overweight: BMI 25 – 29.9
  • Obesity (Class 1): BMI 30 – 34.9
  • Obesity (Class 2): BMI 35 – 39.9
  • Obesity (Class 3): BMI ≥ 40

Limitations of BMI

While BMI can be a useful tool for assessing body weight, it has certain limitations:

  • It does not measure body fat directly: BMI is only an estimate of body fat and does not provide a direct measurement. It is possible for people with a high muscle mass, such as athletes, to have a high BMI without having excess body fat.
  • It does not account for body composition: BMI does not differentiate between muscle and fat, so it may not accurately represent the health of individuals with different body compositions.
  • It may not be accurate for all ethnicities: Studies have shown that BMI may not be equally accurate for all ethnic groups, as different populations may have different body fat distributions and health risks.
  • It may not be accurate for older adults: BMI may not accurately reflect the health of older adults, as they tend to lose muscle mass and bone density with age, which can lead to a lower BMI despite higher body fat levels.

Maintaining a Healthy BMI

To maintain a healthy BMI, it is important to adopt a balanced diet, engage in regular physical activity, and monitor your weight regularly. Here are some tips to help you achieve a healthy BMI:

  • Eat a balanced diet: Include a variety of fruits, vegetables, whole grains, lean proteins, and healthy fats in your diet. Avoid excessive consumption of sugary, fatty, and processed foods.
  • Exercise regularly: Engage in at least 150 minutes of moderate-intensity aerobic activity or 75 minutes of vigorous-intensity aerobic activity per week, along with muscle-strengthening activities on two or more days per week.
  • Monitor your weight: Keep track of your weight and BMI regularly to ensure you stay within a healthy range. Consult a healthcare professional if you are concerned about your weight or BMI.
  • Seek professional help if needed: If you are struggling to maintain a healthy weight or have concerns about your BMI, consult a healthcare professional or registered dietitian for personalized guidance and support.


BMI is a useful tool for assessing body weight and identifying potential health risks related to obesity. However, it is essential to be aware of its limitations and consider other factors, such as body composition and individual health needs, when evaluating your overall health. By maintaining a healthy lifestyle and monitoring your weight, you can work towards achieving and maintaining a healthy BMI.

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