BMI Calculator

Body Mass Index is a simple numerical ratio calculated from height and weight: weight in kilograms divided by height in metres squared. A person weighing 75 kg who is 1.75 m tall has a BMI of approximately 24.5. The metric was developed by Belgian mathematician Adolphe Quetelet in the 1830s and was adopted by health organisations in the 1970s as a cost-effective population-level screening tool.

The World Health Organisation categorises BMI into four ranges: underweight (below 18.5), normal weight (18.5-24.9), overweight (25.0-29.9), and obese (30.0 and above). These categories are used by public health bodies to estimate disease risk at a population level and are widely used as initial screening criteria in clinical settings.

At a population level, higher BMI correlates with increased risk of type 2 diabetes, cardiovascular disease, hypertension, certain cancers, and sleep apnoea. This correlation is why BMI remains in widespread clinical and public health use despite its known limitations. Its main advantage is that it requires only a scale and a tape measure, making it accessible in any setting.

BMI cannot distinguish between fat mass and muscle mass, which means a heavily muscular athlete may be classified as overweight despite having very low body fat. It also does not account for fat distribution — visceral fat around organs is more metabolically dangerous than subcutaneous fat, but both contribute equally to BMI. BMI is a useful starting point for a health conversation, but a healthcare provider will also consider waist circumference, blood pressure, blood glucose, and family history before drawing any conclusions.