What Is Body Mass Index (BMI)?
Body Mass Index (BMI) is a measure used to assess whether a person’s body weight is appropriate for their health by evaluating the ratio of weight to height. BMI is calculated by dividing weight in kilograms by the square of height in meters. The result is used to determine whether an individual falls into the underweight, normal weight, overweight or obese category.
In most people, BMI correlates with body fat: the higher the number, the higher the body fat. Healthcare providers use the BMI calculation together with other tools and tests to evaluate a person’s health status and risks.
High body fat reflected in BMI can lead to heart disease, stroke and type 2 diabetes. Low body fat, on the other hand, is associated with malnutrition. An adequate amount of body fat helps the body absorb vitamins and minerals, provides energy, and protects body temperature and your organs.
How Is Body Mass Index Calculated?
BMI is calculated by dividing a person’s body weight (in kilograms) by the square of their height (in meters). The formula used is BMI = weight (kg) / height (m)².
Steps to Calculate BMI
For example, the BMI of a person weighing 75 kilograms and 1.65 meters tall is calculated as follows:
- First, the square of the height in meters is calculated. In this example, 1.65 x 1.65 = 2.72 m².
- Second, divide the weight in kilograms by the square-meter result. That is, 75 / 2.72. The result is 27.5. This person’s body mass index is determined to be 27.5.
What Should the Body Mass Index Be?
The value produced by the BMI calculation shows what the body mass index should be. The ideal range for a healthy BMI is between 18.5 and 24.9. Those below this value are considered underweight, and those above it are considered overweight.
| Weight Type | Body Mass Index |
|---|---|
| Underweight | < 18.5 |
| Healthy (Normal) | 18.5 - 24.9 |
| Overweight | 25 - 29.9 |
| Obese | 30 - 39.9 |
| Severely Obese | ≥ 40 |
Body Mass Index (BMI) for Women
Ideal BMI values for women are generally similar to those for men, but there may be some variation due to differences in body composition. A higher body fat percentage is generally considered normal in women. The healthy BMI range for women is 18.5 - 24.9.
When assessing BMI in women, periods such as hormonal changes, pregnancy and menopause should also be taken into account. Especially during pregnancy, BMI values may differ from normal, and this is considered natural.
Body Mass Index (BMI) for Men
Ideal BMI values for men are also in the 18.5 - 24.9 range. Men generally have higher muscle mass and a lower body fat percentage than women. For this reason, there may be differences in body composition between a man and a woman with the same BMI value.
When assessing BMI in men, the BMI value may be above the normal range in athletes and individuals who exercise regularly, because their muscle mass may be high. In this case, additional assessments such as body fat percentage measurement are recommended.
Calculating BMI in Children
BMI calculation in children differs from adults. For children, BMI is evaluated by age and gender, using percentile curves. BMI assessment in children must always be performed by a pediatrician.
Important Note: BMI is a general assessment tool and does not take into account factors such as muscle mass, bone density, age and gender. It can be misleading, especially in athletes and individuals with high muscle mass. For accurate information about your health, always consult a doctor.
