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What Is BMI?

BMI is a way to measure how lean or fat a person is based on their height and weight. It helps to estimate how much body tissue a person has. It is a common way to check if a person has a healthy weight for their height. The BMI value is used to put a person into one of four categories: underweight, normal weight, overweight, or obese. These categories depend on where the BMI value falls. Different regions and ages may have different BMI ranges for each category. Some categories may have subcategories like very underweight or extremely obese. Having too much or too little weight can cause health problems, so BMI is a useful way to see if a person needs more tests or actions to improve their health. The table below shows the different BMI categories that the calculator uses.

BMI Table For Adults

This is the WHO’s guide for adult body weight based on BMI values. It applies to both men and women who are 20 years or older.

BMI Category	BMI Range (kg/m2)
Severe Thinness	< 16
Moderate Thinness	16 – 17
Mild Thinness	17 – 18.5
Normal	18.5 – 25
Overweight	25 – 30
Obese Class I	30 – 35
Obese Class II	35 – 40
Obese Class III	> 40

BMI Chart

For those that love to visualize data, you can check out this chart based on data from WHO to see how different weight and height corresponds to different weight class on the BMI scale.

BMI Table For Children

Category	Percentile Range
Underweight	< 5%
Healthy weight	5% – 85%
At risk of overweight	85% – 95%
Overweight	> 95%

BMI formula

Below are the equations used for calculating BMI in the International System of Units (SI) and the US customary system (USC) using a 5’10”, 160-pound individual as an example:

USC Units:BMI = 703 × mass (lbs)height2 (in)= 703 × 160702= 22.96 kgm2SI, Metric Units:BMI = mass (kg)height2 (m) = 72.571.782 = 22.90kgm2