Body Mass Index is your weight in kilograms divided by your height in metres squared. It's a quick screening tool: under 18.5 is underweight, 18.5-24.9 healthy, 25-29.9 overweight, and 30+ obese. BMI doesn't distinguish muscle from fat, so very muscular people can read as overweight despite low body fat. It's useful for populations but a blunt instrument for individuals.
Key points
- Weight (kg) ÷ height (m) squared
- 18.5-24.9 is the healthy range
- Doesn't separate muscle from fat
- Best as a population screen, not a diagnosis