BMI Calculator

What Is Body Mass Index (BMI)?

BMI is a measurement of a person's leanness or corpulence based on their height and weight. It is widely used as a general indicator of whether a person has a healthy body weight for their height. The value obtained from BMI is used to categorize whether a person is underweight, normal weight, overweight, or obese.

While BMI is not a direct measure of body fat, it correlates with more direct measures of body fat such as underwater weighing and dual-energy X-ray absorptiometry (DXA). Due to its low cost and ease of measurement, it remains the primary screening tool used by clinicians worldwide.

BMI Categories for Adults (WHO Standards)

The World Health Organization (WHO) provides standardized categories for adults age 20 and older. These thresholds are linked to the risk of metabolic and cardiovascular diseases:

Asian BMI Standards

Research has shown that many Asian populations have a higher percentage of body fat and higher health risks at lower BMIs than Western populations. The WHO has acknowledged that many countries in Asia have adopted lower thresholds:

• Normal weight: 18.5 – 22.9 kg/m² (vs. 18.5 – 24.9 for general population)
• Overweight: 23.0 – 27.4 kg/m² (vs. 25.0 – 29.9)
• Obese: ≥ 27.5 kg/m² (vs. ≥ 30.0)

Our calculator's "Asian BMI Standards" toggle applies these verified regional thresholds, providing a more accurate health risk assessment for South and East Asian populations.

BMI for Children and Teens (Ages 2–20)

Because children's body compositions change rapidly with age and vary between boys and girls, BMI for children is interpreted using age-and-sex-specific percentiles from the CDC growth charts:

Advanced Metrics: BMI Prime & Ponderal Index

Beyond standard BMI, this calculator provides two advanced anthropometric metrics:

• BMI Prime: The ratio of your measured BMI to the upper limit of the normal range (25 kg/m²). A value of 1.0 means you are exactly at the limit. Values above 1.0 indicate overweight status. This facilitates quick comparison across different population standards.
• Ponderal Index (PI): Also known as Rohrer's Index. Unlike BMI, it cubes height in the denominator, providing better accuracy for people at extreme heights (very tall or very short individuals).

Risks Associated with Being Overweight

According to the CDC, being overweight or obese increases the risk of:

• High blood pressure and higher LDL cholesterol
• Type 2 diabetes and coronary heart disease
• Stroke and gallbladder disease
• Osteoarthritis and sleep apnea
• Certain cancers (endometrial, breast, colon, kidney)
• Clinical depression and reduced quality of life

Risks Associated with Being Underweight

Being underweight also carries health risks including:

• Malnutrition, vitamin deficiencies, and anemia
• Osteoporosis and weakened immune function
• Reproductive issues and hormonal imbalances in women
• Growth and development issues in children

Limitations of BMI

BMI is only an estimate that cannot take body composition into account. It cannot distinguish between muscle mass and fat mass. Athletes and bodybuilders may be classified as overweight or obese despite having low body fat. For a more complete picture, consider using a Body Fat Calculator or Waist-to-Hip Ratio Calculator alongside BMI.

Frequently Asked Questions