Body Mass Index (BMI) Calculator

What is Body Mass Index (BMI)?

Body Mass Index (BMI) is an internationally recognized anthropometric screening metric established by Belgian mathematician Adolphe Quetelet. It quantifies the relationship between an individual's mass and height to categorize tissue mass (muscle, fat, and bone) into general wellness brackets recognized by the World Health Organization (WHO) and Centers for Disease Control and Prevention (CDC).

The Standard Mathematical BMI Formulas

Depending on whether you use metric or imperial measurements, the formulas are:

Official WHO Weight Classifications

• Underweight: BMI less than 18.5
• Normal Weight (Healthy): BMI 18.5 – 24.9
• Overweight: BMI 25.0 – 29.9
• Obesity Class I: BMI 30.0 – 34.9
• Obesity Class II: BMI 35.0 – 39.9
• Obesity Class III (Severe): BMI 40.0 or greater

Step-by-Step Example Calculation

Consider an adult who is 175 cm tall (1.75 meters) and weighs 70 kg:

1. Square the height in meters: \(1.75 \times 1.75 = 3.0625\).
2. Divide weight by height squared: \(70 / 3.0625 \approx 22.86\).
3. Rounding gives a BMI of 22.9.

A BMI of 22.9 falls comfortably into the Normal Weight category (18.5 - 24.9), indicating a proportional weight-to-height balance.

Important Limitations of BMI

While BMI provides a fast, non-invasive public health indicator, it does not directly measure body fat percentage. Athletes and bodybuilders with high lean muscle mass may register as "overweight" or "obese" despite extremely low visceral fat. Conversely, elderly individuals with age-related muscle loss (sarcopenia) may score a "normal" BMI while carrying excessive adipose tissue.

Frequently Asked Questions (FAQ)