BMI calculator – what you need to know about body mass index calculation?

How can you calculate your BMI?

To calculate BMI you only need two pieces of information: your weight in kilograms and your height in meters.

The BMI calculator formula is: BMI = weight (kg) / (height (m))²

In words: weight divided by the square of the height measured in meters.

So if you weigh 70 kilograms and are 170 centimeters tall, first convert your height to meters (1.7 m), then multiply it by itself (1.7 × 1.7 = 2.89).

Finally divide your weight (70 kg) by this number (70 ÷ 2.89 = 24.2). The resulting value of 24.2 is your body mass index.

What do BMI values mean?

The categories defined by the World Health Organization (WHO) primarily apply to European populations; different regions may use different cutoff values.

Based on BMI you can classify yourself into the following categories:

• BMI under 18.5: Underweight.
• BMI 18.5–24.9: Normal weight.
• BMI 25.0–29.9: Overweight.
• BMI 30.0–34.9: Obesity class I.
• BMI 35.0–39.9: Obesity class II.
• BMI over 40.0: Obesity class III (severe).

Practical use of the BMI calculator

Assessing health risks

BMI can help you assess health risks associated with obesity or underweight.

A high BMI is associated with a higher prevalence of many chronic diseases, such as cardiovascular diseases, type 2 diabetes, or certain cancers.

Conversely, a low BMI may indicate undernutrition, hormonal problems, or other health concerns.

Monitoring weight changes

The BMI calculator can be an excellent tool for tracking weight changes.

If you start a diet or aim to build muscle, regular BMI calculations can help you objectively follow changes.

However, it is important to know that when evaluating weight changes you should also consider other measures, such as waist-to-hip ratio or body fat percentage.

Limitations and shortcomings of the BMI calculator

Ignoring body composition

One of the biggest shortcomings of BMI is that it does not take your body composition into account. It does not distinguish between muscle mass and fat tissue.

Therefore, a regularly training, muscular athlete may be classified as overweight or even obese by BMI, even though they are actually healthy and fit.

Similarly, a person with a seemingly normal BMI may have an excessively fatty body composition if they have little muscle.

Age and sex differences

BMI does not take into account your age or sex. Yet optimal body composition changes significantly with age and differs between men and women.

For example, in older age it is natural for muscle mass to decrease and body fat percentage to increase, which BMI cannot adequately reflect.

Ignoring body frame and genetic differences

Your body build and genetic predispositions can significantly affect what is a healthy weight for you.

The BMI calculator does not account for your bone density, bone thickness, or general body build. For example, a person with a broad skeleton and a more robust build may naturally have a higher body weight without this representing a health risk.

Correct use and interpretation of the BMI calculator

BMI is a useful starting point for assessing your body's condition, but it's important to understand its limitations.

It is a simple and quick method that can help with basic orientation, but it cannot replace professional medical or nutritional advice.

BMI should always be evaluated together with other measures, and you should consider your individual characteristics. If you want to change your weight, primarily seek professional help, who can create a personalized program for you.

The BMI calculator mainly serves to draw your attention to possible risks and to provide a starting point for adopting a healthier lifestyle.