What BMI tells you
BMI is your weight in kilograms divided by your height in metres squared. The WHO uses these adult ranges: under 18.5 underweight, 18.5 to 24.9 healthy, 25 to 29.9 overweight, 30 and over obese.
BMI does not tell muscle from fat, and it is not meant for children, pregnancy or very muscular people. Waist size adds useful detail.