BMI Calculator
Body Mass Index (BMI) is an indicator used to measure the relationship between a person's weight and height. The BMI formula calculates by dividing a person's weight (in kilograms) by the square of their height (in meters). Typically, BMI is used to assess whether a person is underweight, normal weight, overweight, or obese.
BMI =
BMI Prime=
Adult BMI
Since BMI does not account for body fat percentage, a person with a BMI classified as overweight may not necessarily be obese. For instance, athletes may have a BMI over 30 due to a higher proportion of muscle mass, without needing to lose weight if their body fat percentage is low. This indicates that BMI is only a rough indicator and cannot fully reflect body composition and health status.
BMI prime allows us to quickly assess the extent to which a person's BMI differs from the upper limit of normal BMI. It also enables comparisons between populations with different upper BMI limits. A BMI prime less than 0.74 classifies a person as underweight; from 0.74 to 1 as normal; greater than 1 as overweight, and greater than 1.2 as obese.
| Status | BMI (kg/m2) | BMI Prime |
|---|---|---|
| Severe Thinness | <15 | <0.6 |
| Moderate Thinness | 15 - 16 | 0.6 - 0.64 |
| Mild Thinness | 16 - 18.5 | 0.64 - 0.74 |
| Normal | 18.5 - 25 | 0.74 - 1.0 |
| Overweight | 25 -30 | 1.0 - 1.2 |
| Obese Class I | 30 - 35 | 1.2 - 1.4 |
| Obese Class II | 35 - 40 | 1.4 - 1.6 |
| Obese Class III | >1.6 | >40 |
Limitations of BMI
Although BMI is a commonly used indicator to assess an individual's overall body weight status, it also has some limitations to consider. BMI primarily reflects total body weight and cannot distinguish between different tissues (such as fat, muscle, and organs). Therefore, individuals with the same BMI may have different levels of body fat. Additionally, BMI does not provide information about fat distribution, such as whether fat tissue is concentrated in the abdomen or limbs. These factors are important and closely related to health status and disease risk.
While BMI has been widely used as an indicator of obesity in the past, we now have a clearer understanding of its limitations. Therefore, healthcare professionals typically consider BMI along with other indicators, such as waist circumference, body fat percentage, lifestyle factors, and family medical history, when assessing an individual's health status. This helps to provide a more comprehensive evaluation of an individual's health and develop more tailored health management plans.