Calculate your Body Mass Index — the classic weight screening metric used by healthcare professionals worldwide.
BMI does not distinguish between muscle and fat, or account for fat distribution. It may overestimate risk in muscular individuals and underestimate it in others.
Body Mass Index (BMI) is a numerical value calculated from your weight and height. Developed by Belgian mathematician Adolphe Quetelet in the early 19th century, it has been used for over 200 years as a simple proxy for body fatness at the population level.
BMI is widely used by health organisations including the World Health Organisation (WHO) and national health services around the globe as a first-line screening tool for weight-related health risks. However, it has significant limitations that are important to understand.
Metric: BMI = Weight (kg) ÷ Height (m)²
Imperial: BMI = (Weight (lbs) × 703) ÷ Height (inches)²
For example, a person weighing 75 kg and standing 1.75 m tall has a BMI of 75 / (1.75 × 1.75) = 24.5, placing them in the normal weight category.
| BMI Range | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Normal weight |
| 25.0 – 29.9 | Overweight |
| 30.0 and above | Obese |
BMI has well-documented shortcomings. It cannot distinguish between lean mass (muscle, bone) and fat mass. This means highly muscular individuals — athletes, manual labourers — are often classified as overweight or obese despite having low body fat. Conversely, older adults who have lost muscle mass may receive a "normal" BMI while carrying excess fat.
BMI also ignores fat distribution. Two people with identical BMIs can have dramatically different risk profiles depending on whether their fat is stored around the abdomen or on the hips and thighs. This is why metrics like WHtR and waist-to-hip ratio are increasingly recommended alongside BMI.
Furthermore, BMI thresholds were developed primarily using data from European populations and may not accurately reflect risk in people of South Asian, East Asian, or African descent.
Despite its limitations, BMI remains a quick, free, and universally understood screening tool. It is most useful at the population level for tracking trends, and at the individual level as a starting point — not a final answer — in health assessment. For a more complete picture, combine BMI with waist circumference, WHtR, blood pressure, and blood chemistry.
A BMI between 18.5 and 24.9 is considered normal weight. Below 18.5 is underweight, 25–29.9 is overweight, and 30 or above is classified as obese by the WHO.
BMI cannot distinguish between muscle and fat, or account for fat distribution. Athletes, older adults, and people of different ethnicities may receive misleading classifications.
BMI equals your weight in kilograms divided by your height in metres squared. In imperial units, multiply weight in pounds by 703 and divide by height in inches squared.
Research suggests WHtR is a better predictor of health risk because it captures abdominal fat. BMI is still useful as a basic screening tool but ideally should be combined with WHtR or waist measurements.