BMI Calculator
Calculate your Body Mass Index (BMI) instantly by entering your weight and height. Use it to screen for underweight, healthy weight, overweight, or obesity categories as defined by the WHO.
About this calculator
BMI (Body Mass Index) is a simple screening metric that relates body weight to height. The formula is BMI = weight / (height / 100)², where weight is in kilograms and height is converted from centimeters to meters before squaring. The result is expressed in kg/m². WHO classifies BMI below 18.5 as underweight, 18.5–24.9 as healthy, 25–29.9 as overweight, and 30 or above as obese. Because BMI does not directly measure body fat or account for muscle mass, age, or sex, it is best used as an initial screening tool rather than a definitive health diagnosis. Athletes, for example, may have a high BMI due to muscle while remaining metabolically healthy.
How to use
Suppose you weigh 75 kg and are 175 cm tall. Step 1: Convert height to meters — 175 / 100 = 1.75 m. Step 2: Square the height — 1.75² = 3.0625. Step 3: Divide weight by that value — 75 / 3.0625 ≈ 24.49. Your BMI is approximately 24.5, which falls in the 'Healthy Weight' range (18.5–24.9). Enter your own numbers in the fields above to get your result instantly.
Frequently asked questions
What is a healthy BMI range for adults?
For most adults, a BMI between 18.5 and 24.9 is considered healthy by the World Health Organization. A BMI below 18.5 is classified as underweight, 25–29.9 as overweight, and 30 or above as obese. These thresholds are population-level guidelines and may not apply equally to all ethnicities — for example, some Asian health organizations use lower cutoffs. Always consult a healthcare professional for a full health assessment.
Why does BMI not account for muscle mass?
BMI uses only total body weight and height, making no distinction between fat mass and lean muscle mass. A highly muscular athlete can have a BMI in the overweight or obese range despite having very low body fat. Conversely, someone with a normal BMI can still carry an unhealthy proportion of body fat — a condition sometimes called 'normal weight obesity.' For a more complete picture, consider pairing BMI with body fat percentage or waist circumference measurements.
How is BMI calculated differently for children versus adults?
For adults aged 20 and over, BMI is interpreted using fixed thresholds regardless of age or sex. For children and teenagers aged 2–19, BMI is calculated the same way but interpreted using age- and sex-specific percentile charts, since body fat naturally changes with growth. A child is considered obese if their BMI is at or above the 95th percentile for their age and sex. This calculator is designed for adult use; consult a pediatrician for child BMI interpretation.