How it works
BMI is your weight in kilograms divided by your height in metres squared. The categories are the WHO adult ranges: under 18.5 underweight, 18.5-24.9 healthy weight, 25-29.9 overweight, 30 and over obesity.
Waist-to-height ratio
Your waist divided by your height. UK NICE guidance suggests keeping your waist to less than half your height (a ratio under 0.5), because fat around the middle carries more health risk than BMI alone shows. Measure around your middle, halfway between your lowest rib and the top of your hip bone.
Limits
BMI doesn't separate muscle from fat, and the categories aren't meant for children, pregnancy, or very muscular people.
