Body Mass Index (BMI) is a screening measurement that relates your weight to your height using the formula weight (kg) divided by height (m) squared. It's widely used by health organizations as a quick, low-cost screening tool, but it doesn't distinguish between muscle and fat mass, so athletes and very muscular individuals often show as 'overweight' despite having low body fat. This calculator supports both imperial (feet/inches, pounds) and metric (cm, kg) units and categorizes your result using standard WHO BMI ranges.