What Is Body Mass Index (BMI)?
Body Mass Index (BMI) is an international measure used to assess whether a person's weight is appropriate for their height.
BMI is used to estimate obesity risk, detect excess weight, track body weight and evaluate health risks.
It does not diagnose disease on its own, because it ignores muscle mass, body fat and body type. Clinicians therefore combine BMI with waist circumference, body fat and metabolic tests.
How Is BMI Calculated?
Body mass index is calculated with this formula:
BMI = Weight (kg) / Height² (m²)
Example
Height: 175 cm · Weight: 75 kg → 75 ÷ (1.75 × 1.75) = 24.49. Result: Normal weight.
BMI Calculation Formula
BMI = Weight / Height²
BMI = Weight / Height²
Height must be in metres. Example: 170 cm → 1.70 m.
BMI Values Table
| BMI | Status |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Normal |
| 25 – 29.9 | Overweight |
| 30 – 34.9 | Class I obesity |
| 35 – 39.9 | Class II obesity |
| 40+ | Morbid obesity |
What Do BMI Results Mean?
Below 18.5 (Underweight)
Your body weight is below the ideal range. Undernutrition, vitamin deficiencies and weaker immunity may occur.
18.5 – 24.9 (Normal)
This is the generally healthy range. Maintain it with balanced nutrition and regular exercise.
25 – 29.9 (Overweight)
Risk of heart disease, hypertension and type 2 diabetes begins to rise.
30 and above (Obese)
Obesity is a major risk factor for many chronic diseases. Consulting a health professional is recommended.
What Is an Ideal BMI?
According to the World Health Organization, an ideal adult BMI is between 18.5 and 24.9. This range represents a lower general health-risk group.
BMI in Women
Hormonal changes, pregnancy, menopause and age can make fat distribution in women different from men.
Therefore BMI should be interpreted with waist circumference, body fat and muscle mass.
BMI in Men
Men often carry more muscle, so some athletes may show a high BMI while body fat remains normal.
Judging health from BMI alone is not accurate.
BMI in Children
Adult classification is not used for people under 18.
In children, age, sex and percentile charts are used instead.
Limitations of BMI
- Does not measure muscle mass
- Does not show body fat percentage
- Can mislead for athletes
- May be less accurate in older adults
Therefore it is not the only criterion in professional assessment.
Tips for Reaching a Healthy Weight
- Increase your daily movement.
- Exercise at least 150 minutes per week.
- Reduce processed foods.
- Limit sugary drinks.
- Drink enough water.
- Sleep regularly.
- Eat fibre-rich foods.
Frequently Asked Questions
At what BMI are you considered obese?
Values of 30 and above are classified as obesity.
Why does BMI matter?
It helps identify excess weight and obesity risk early.
Is BMI enough on its own?
No. It should be combined with waist circumference, body fat and muscle mass.
Is BMI accurate for athletes?
Not always. People with high muscle mass may show a high BMI while body fat is low.
Are BMI and ideal weight the same?
No. BMI only relates height and weight. Ideal weight also depends on age, sex, muscle mass and lifestyle.