How to Calculate BMI (Body Mass Index)
The Body Mass Index (BMI) is the most common international measurement adopted by the World Health Organization (WHO) to diagnose and monitor a person's degree of obesity, overweight or thinness. This is a quick screening metric that helps identify health risks associated with body weight.
In this complete guide, we explain the mathematical formula, how to interpret the result in the WHO table and how our BMI Calculator can do the math for you instantly.
The BMI Formula
The BMI calculation is simple and only takes into account your weight (in kilograms) and your height (in meters). The standard mathematical formula is:
BMI = Weight / (Height * Height)
Practical Calculation Example
If you weigh 70 kg and are 1.75 m tall, your BMI calculation will be:
- Multiply the height by itself: $1,75 \times 1,75 = 3,0625$
- Divide the weight by this result: $70 \div 3,0625 = 22,86$
- Your BMI is 22.9 kg/m² (classified as normal weight).
WHO Classification Table
After finding the numerical value of your BMI, you can consult the official World Health Organization (WHO) weight classification table for adults:
| BMI range | Classification | Health Risk Level |
|---|---|---|
| Less than 18.5 | Underweight | Low (risk of malnutrition) |
| Between 18.5 and 24.9 | Normal weight | Minimum (healthy range) |
| Between 25.0 and 29.9 | Overweight (Pre-obesity) | Moderate |
| Between 30.0 and 34.9 | Obesity Grade I | High |
| Between 35.0 and 39.9 | Obesity Grade II | Very High |
| Greater than or equal to 40.0 | Obesity Grade III (Morbid) | Severus |
BMI Limitations: What You Need to Know
Although BMI is an excellent statistical tool for population screening, it has important limitations when assessed individually:
- Does not distinguish muscle mass from fat: Bodybuilding athletes or bodybuilders may have a high BMI (indicating overweight or obesity) due to the high amount of muscle, even though they have a very low percentage of body fat.
- Does not indicate fat distribution: BMI does not differentiate peripheral fat (below the skin) from visceral fat (accumulated around internal organs, in the abdominal region), which is the type of fat associated with heart attacks and type 2 diabetes.
- Not applicable to everyone: Pregnant women, elderly people who have lost muscle mass, children who are growing rapidly and people with severe fluid retention should not use the standard adult BMI table.
Calculate your BMI Right Now
To obtain your result without having to do the math at the tip of a pencil, access our free tool. It calculates your BMI, tells you your ideal weight and presents the official classification. Click here to access our BMI Calculator!