BMI Calculator - Calculate Your Body Mass Index

What Is Body Mass Index (BMI)?

Body Mass Index (BMI) is a widely used metric for assessing whether a person has a healthy body weight for a given height. Originally known as the Quetelet Index, it was developed in the 19th century by Belgian statistician Adolphe Quetelet. Today, it serves as a fundamental screening tool for the World Health Organization (WHO) and healthcare providers globally.

While BMI is not a direct measure of body fat, it correlates moderately well with direct measures like skinfold thickness measurements, bioelectrical impedance, and underwater weighing. Because it is inexpensive and easy to calculate, it remains the standard first step in evaluating weight-related health risks.

The Science Behind the Number

The BMI calculation represents the relationship between mass and height squared (kg/m²). This relationship suggests that for a person to maintain the same body shape while growing taller, their weight should increase proportional to the square of their height. When the result deviates significantly from the "Normal" range, it may indicate that a person is carrying too much or too little weight for their frame.

Health Risks by Category

Your BMI score places you into specific categories, each associated with different health implications.

• Underweight (BMI < 18.5): Being underweight can indicate malnutrition, eating disorders, or underlying illness. Risks include weakened immune function, osteoporosis (bone fragility), anemia, and fertility issues.
• Normal Weight (BMI 18.5 – 24.9): This range is statistically associated with the lowest incidence of serious illness and mortality. Maintaining a weight in this zone is ideal for long-term heart and joint health.
• Overweight (BMI 25.0 – 29.9): People in this range carry excess weight that may increase the workload on the heart and joints. It is a warning sign to adopt healthier lifestyle habits to prevent progression to obesity.
• Obese (BMI ≥ 30.0): Obesity is a chronic condition linked to serious health complications, including Type 2 diabetes, coronary heart disease, stroke, sleep apnea, and osteoarthritis. It is often subdivided into Class I, II, and Class III (severe or morbidly obese).

BMI Chart - Body Mass Index Reference

Use this BMI chart to quickly reference standard WHO body mass index categories for adults (age 20+). This BMI chart for adults shows the BMI range for each category and associated health risks.

BMI Calculator for Men, Women, and Children

BMI Calculator for Men and Women

Is BMI calculated differently for men and women? The BMI calculator for men and the BMI calculator for women use the exact same formula. The standard body mass index calculation applies to all adults regardless of sex. However, the interpretation can vary subtly because women naturally carry more body fat than men at the same BMI score.

BMI Calculator for Kids and Teens

For a BMI calculator for children under 20, the calculation formula is the same, but the result is interpreted using BMI Percentiles relative to age and sex. A 10-year-old boy with a BMI of 23 might be considered obese, while an adult with the same BMI is normal. This BMI calculator is designed primarily for adults (age 20+), but can be used as a general BMI calculator for kids with the understanding that pediatric interpretation differs.

BMI Calculator in KG (Metric)

Our BMI calculator in kg uses the metric system: weight in kilograms (kg) and height in centimeters (cm). This is the most widely used BMI calculation method globally. The formula is: BMI = Weight (kg) / [Height (m)]²

Imperial BMI Calculator

The imperial BMI calculator uses pounds (lb) for weight and feet/inches for height. It multiplies the result by 703 to convert to the standard BMI scale, making it just as accurate as the metric version.

Why BMI Isn't the Full Story

While BMI is an excellent screening tool for populations, it has blind spots when assessing individuals:

• Muscle Mass (Athletes & Bodybuilders): Muscle tissue is dense. Bodybuilders, weightlifters, and athletes often classify as "Overweight" or "Obese" on a standard calculator despite having very low body fat percentages.
• Bone Density: Individuals with dense, heavy bone structures may register a higher BMI without being unhealthy.
• Fat Distribution: BMI does not track where fat is stored. Visceral fat (around the organs) is more dangerous than subcutaneous fat, but BMI treats all weight equally.

For a complete health profile, doctors often combine BMI with Waist-to-Hip Ratio, skinfold measurements, and blood tests. If you want to estimate your actual fat percentage, try our Body Fat Calculator instead.