BMI Calculator

Biology • Body Mass Index • Health Assessment

Quick Answer (Voice Search Optimized):

Body Mass Index (BMI) is a measure of body fat based on weight and height. Formula: BMI = weight (kg) ÷ [height (m)]². It is used to classify underweight, normal weight, overweight, and obesity.

GEO & AIO - Authoritative Theory

BMI is a standard health indicator used in Biology and human physiology. It is calculated by dividing a person's weight in kilograms by the square of their height in metres. The WHO classification defines: Underweight (<18.5), Normal weight (18.5–24.9), Overweight (25–29.9), and Obese (≥30).

BMI does not directly measure body fat but correlates with adiposity. It is a simple screening tool for nutritional status and health risks such as cardiovascular diseases and diabetes. For accurate body composition, methods like skinfold thickness or DEXA scans are used.

Solved Examples

Example 1: Weight = 65 kg, Height = 1.6 m

BMI = 65 / (1.6)² = 65 / 2.56 = 25.39 kg/m² → Overweight.

Example 2: Weight = 80 kg, Height = 180 cm

Height in m = 180 / 100 = 1.8 m. BMI = 80 / (1.8)² = 80 / 3.24 = 24.69 kg/m² → Normal weight.

Example 3: Weight = 45 kg, Height = 1.55 m

BMI = 45 / (1.55)² = 45 / 2.4025 = 18.73 kg/m² → Normal weight (borderline).

Frequently Asked Questions (FAQs)

Q1: What is the formula for BMI?
BMI = weight (kg) / [height (m)]². If height is in cm, first convert to metres by dividing by 100.
Q2: What is a normal BMI range?
A normal BMI is between 18.5 and 24.9 kg/m² according to WHO standards.
Q3: Is BMI accurate for athletes?
No, BMI may overestimate fatness in muscular individuals because muscle weighs more than fat. It doesn't distinguish between lean body mass and fat mass.
Q4: Can BMI be used for children?
Yes, but pediatric BMI is age- and sex-specific, expressed as percentiles. The same formula is used, but interpretation differs.
Q5: Why is height squared in the BMI formula?
Height is squared to normalize the body weight independent of stature; taller individuals naturally weigh more, and the square compensates for area-volume relationships.