How it works
BMI is weight in kilograms divided by height in meters squared. Imperial inputs are converted to metric first using the exact pound-to-kilogram and inch-to-meter ratios, so the result is identical either way.
Reading the category
The standard adult ranges are under 18.5 for underweight, 18.5 to 25 for normal weight, 25 to 30 for overweight, and 30 and above for obese. These thresholds come from World Health Organization guidance for the general adult population.
What BMI does not capture
BMI cannot tell muscle from fat, so it can read high for very muscular people and normal for people with low muscle mass and high body fat. It is a quick, population-level screening tool, not an individual diagnosis.