What is BMI?
Body mass index (BMI) relates your weight to your height. It's a quick, inexpensive way to classify weight into ranges and spot possible risks, which is why it's used as a first filter in consultations and studies.
How it's calculated
Divide your weight in kilograms by your height in meters squared.
FormulaBMI = weight (kg) ÷ height² (m)
Example80 kg ÷ (1.65 × 1.65) = 29.4
| Category | BMI (adults) |
|---|---|
| Underweight | Below 18.5 |
| Healthy weight | 18.5 – 24.9 |
| Overweight | 25 – 29.9 |
| Obesity | 30 or higher |
Source: Centers for Disease Control and Prevention (CDC).
What BMI doesn't tell you
BMI doesn't distinguish between fat and muscle, and it doesn't show where fat is stored. Two people with the same BMI can have very different metabolic health.
- It doesn't separate muscle mass from fat
- It doesn't show how abdominal fat is distributed
- It doesn't reflect glucose, blood pressure or habits
BMI is an initial screening tool, not a diagnostic test.
What else to measure
Waist circumference
Reflects abdominal fat, which is linked to metabolic risk.
Body composition
Separates fat, muscle and water using a bioimpedance scale.
Glucose and A1c
Show how your body processes carbohydrates.
