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How To Calculate Body Mass Index: Online BMI Calculator

If you want to estimate your body fat and determine if you are underweight, at a healthy weight, overweight, or obese, then calculating your body mass index (BMI) can be a useful tool. 

The formula for calculating BMI is simple and involves using your weight (in pounds or kilograms) and height (in inches or meters). BMI can also help assess your risk for certain health conditions, such as heart disease. However, it is important to keep in mind that BMI can mean different things depending on your age or level of fitness

In this article, you will learn how to calculate BMI and what it can tell you about your health. You will also learn about the advantages and disadvantages of BMI scores and what they can and cannot reveal.

BMI Calculation

You can easily calculate your BMI using either the metric system (kilograms and meters) or the imperial system (pounds and inches) with simple math skills, either by hand or with a calculator.

Here are the formulas that describe the calculations:

(kilograms, meters)
(pounds, inches)
Formula: weight (kg) / height (m2)Formula: weight (lbs) / height (in2) x 703
The formula for BMI is weight in kilograms (kg) divided by height in meters squared (m2).The formula for BMI is weight in pounds (lbs) divided by inches squared (in2). The total is then multiplied by 703.

Understanding BMI Scores

Body mass index, or BMI, is a measurement used to determine whether an individual’s weight is healthy or not. The BMI score is calculated using a formula that considers a person’s height and weight. The optimum range for a healthy BMI is between 18.5 and 24.9. If the score is below 18.5, the person is considered underweight, and if it’s above 24.9, they are considered overweight. 

BMI scores are further broken down into the following categories:

  • Underweight: BMI less than 18.5
  • Normal weight: BMI of 18.5 to 24.9
  • Overweight: BMI of 25 to 29.9
  • Obesity: BMI of 30 or higher

Obesity can also be divided into three categories based on BMI:

  • Class 1 (mild obesity): BMI 30 to 34.9
  • Class 2 (moderate obesity): BMI 35 to 39.9
  • Class 3 (severe obesity): BMI of 40 or higher

It’s important to note that BMI is not a perfect health measure and should be used with other indicators, such as waist circumference, to assess an individual’s overall health status.

BMI Chart for Adults

BMI Chart for Children

BMI Categories and Ranges

The World Health Organization (WHO) provides standard BMI ranges for adults. These ranges vary from severe thinness to obese class III, with corresponding BMI values. For example, a BMI below 16 is classified as severe thinness, while a BMI above 40 is classified as obese class III. Similar classifications exist for children and teens, with percentile ranges used to categorize BMI values based on age and sex.

How BMI Affects Health

Excess body fat increases the risk of various health issues. Overweight or obese people are more likely to develop diseases such as:

Who Shouldn’t Use BMI?

BMI should not be used in children under 2 years of age. The American Academy of Pediatrics recommends using BMI to screen for overweight and obesity in children beginning at 2 years old.


In conclusion, BMI is a valuable tool for assessing healthy body weight, but it should be used in conjunction with other measures to provide a comprehensive assessment of an individual’s health status. Regular monitoring of BMI and consultation with a healthcare professional can help individuals maintain a healthy weight and reduce the risk of associated health problems.

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