BMI calculator

What is BMI?

Body Mass Index (BMI) is a simple numerical measure that relates body weight to height. It was developed by Belgian mathematician Adolphe Quetelet in the 19th century and has since become the most widely used screening tool to identify potential weight-related health risks in adults.

The formula is straightforward: divide your weight in kilograms by the square of your height in metres. The result places you into one of four broad categories defined by the World Health Organization:

• Under 18.5 — underweight
• 18.5 – 24.9 — normal weight
• 25 – 29.9 — overweight
• 30 and above — obese

BMI is a population-level tool, not a clinical diagnosis. It does not measure body fat directly and cannot distinguish between muscle mass and fat mass. Use it as a starting point, not the final word on your health.

Frequently asked questions

What is a healthy BMI?

According to the World Health Organization (WHO), a BMI between 18.5 and 24.9 is considered normal weight for adults. Below 18.5 is classified as underweight, 25–29.9 as overweight, and 30 or above as obese.

What does BMI not measure?

BMI does not distinguish between muscle mass and body fat. A highly muscular person may have a high BMI without excess fat. It also does not account for how fat is distributed around the body, which affects health risk. For a fuller picture, consider waist circumference or body fat percentage alongside BMI.

Is BMI accurate for everyone?

BMI is a useful screening tool for most adults, but it has known limitations for athletes, older adults, and some ethnic groups. Research suggests that people of Asian descent may face increased health risks at lower BMI thresholds. Always interpret your result in the context of your overall health.

How is BMI calculated?

BMI is calculated by dividing your weight in kilograms by the square of your height in metres: BMI = kg / m². For example, a person who is 175 cm tall and weighs 70 kg has a BMI of 70 / (1.75 × 1.75) = 22.9.