Last updated: 3 October 2026
Reviewed by Jordan Morley, FA Level 2 Football Coach
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.
- 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
In practice
BMI remains widely used as a quick population-level screening tool, but sports scientists and doctors increasingly flag its limitations for athletes — a muscular rugby player or powerlifter can register as 'overweight' or 'obese' by BMI despite having low body fat, because the formula can't distinguish muscle mass from fat mass.
FAQ
Is BMI accurate for athletes?
Often not — BMI doesn't distinguish muscle from fat, so muscular athletes frequently show an inflated BMI that doesn't reflect their actual body composition or health.
What's a better measure of body composition than BMI?
Body fat percentage (via skinfold calipers, bioelectrical impedance or DEXA scanning) gives a far more accurate picture of an individual's actual composition than BMI alone.