BMI Calculator
Calculate your Body Mass Index (BMI) instantly. Find out if your weight is in a healthy range for your height, with personalized category interpretation and health recommendations.
BMI Calculator
What is Body Mass Index (BMI)?
Body Mass Index, commonly known as BMI, is a numerical value derived from an individual's height and weight. It serves as a simple, widely-used screening tool to categorize whether a person has a healthy body weight for their height. Developed in the 1830s by Belgian mathematician Adolphe Quetelet, BMI has become the standard metric used by healthcare organizations worldwide, including the World Health Organization (WHO) and the Centers for Disease Control and Prevention (CDC), to assess population health and identify potential weight-related health risks.
The appeal of BMI lies in its simplicity — it requires only two measurements (height and weight) and provides a single number that can be easily interpreted against established categories. While BMI does not directly measure body fat or overall health, research has shown strong correlations between BMI values and the risk of chronic conditions such as heart disease, type 2 diabetes, high blood pressure, and certain cancers. This makes it a valuable initial assessment tool that healthcare providers use alongside other measurements to evaluate a patient's health status.
It is important to understand that BMI is a screening tool, not a diagnostic instrument. A high BMI does not necessarily mean someone is unhealthy, just as a normal BMI does not guarantee good health. Factors such as muscle mass, bone density, age, sex, and ethnicity all influence how BMI relates to actual body composition. For example, athletes with high muscle mass may have BMIs in the "overweight" category despite having low body fat. Similarly, older adults may have normal BMIs but reduced muscle mass and increased body fat. Therefore, BMI should be considered alongside other health indicators for a comprehensive assessment.
BMI Formula and Calculation
Imperial: BMI = 703 × weight(lbs) / height(in)²
For a person weighing 70 kg and 170 cm tall:
- BMI = 70 / (1.70)² = 70 / 2.89 = 24.2
- Category: Normal weight (18.5-24.9)
- Healthy weight range for 170 cm: 53.5 kg - 72.0 kg
BMI Categories (WHO Classification)
| BMI Range | Category | Health Risk |
|---|---|---|
| Below 18.5 | Underweight | Increased |
| 18.5 - 24.9 | Normal weight | Lowest |
| 25.0 - 29.9 | Overweight | Increased |
| 30.0 - 34.9 | Obese (Class I) | High |
| 35.0 - 39.9 | Obese (Class II) | Very High |
| 40.0+ | Obese (Class III) | Extremely High |
Limitations of BMI
While BMI is useful for population-level screening, it has several limitations. It does not distinguish between fat mass and lean mass (muscle, bone, organs), so muscular individuals may be misclassified as overweight. BMI also does not account for fat distribution — abdominal fat (visceral fat) poses greater health risks than fat stored in hips and thighs. Additionally, BMI may underestimate body fat in older adults who have lost muscle mass. For a more complete health picture, consider measuring waist circumference, body fat percentage, and consulting with a healthcare professional.