How to Use This BMI Calculator
Select US Units or Metric Units, then enter your age, gender, height, and weight. Click Calculate to see your BMI on the gauge chart along with your weight classification and healthy weight range.
BMI Calculator
Enter your age, gender, height, and weight to calculate your Body Mass Index.
BMI Classification (Adults, WHO)
World Health Organization standards for adults age 20 and older.
| Classification | BMI Range (kg/m²) |
|---|---|
Severe Thinness | < 16 |
Moderate Thinness | 16 – 17 |
Mild Thinness | 17 – 18.5 |
Normal | 18.5 – 25 |
Overweight | 25 – 30 |
Obese Class I | 30 – 35 |
Obese Class II | 35 – 40 |
Obese Class III | > 40 |
BMI Classification (Children & Teens, Age 2–20)
CDC BMI-for-age percentile standards.
| Category | Percentile Range |
|---|---|
Underweight | < 5th |
Healthy weight | 5th – 85th |
At risk of overweight | 85th – 95th |
Overweight | > 95th |
What is BMI?
Body Mass Index (BMI) is a number calculated from a person's weight and height. It provides a reliable indicator of body fatness for most people and is used to screen for weight categories that may lead to health problems. BMI does not directly measure body fat, but research has shown that BMI correlates with more direct measures of body fat.
The BMI formula is: BMI = weight (kg) / height (m)². In US units: BMI = 703 × weight (lbs) / height (in)². For example, a person who is 5'9" (175 cm) and weighs 170 lbs (77 kg) has a BMI of approximately 25.1, which falls in the "Normal weight" range.
BMI Categories (WHO Standard)
The World Health Organization defines BMI ranges as follows: Underweight is below 18.5; Normal weight is 18.5–24.9; Overweight is 25.0–29.9; and Obese is 30.0 and above. Obesity is further divided into Class I (30–34.9), Class II (35–39.9), and Class III (40+).
BMI Prime & Ponderal Index
BMI Prime is the ratio of your BMI to the upper limit of the normal range (25 kg/m²). A BMI Prime of 1.0 means you are exactly at the upper boundary of normal weight. Values below 0.74 indicate underweight; above 1.0 indicates overweight.
The Ponderal Index (kg/m³) is similar to BMI but uses the cube of height instead of the square. It is more reliable for very tall or very short individuals.
Limitations of BMI
BMI is a screening tool, not a diagnostic measure. It does not account for muscle mass, bone density, age, sex, or ethnic differences in body composition. Athletes with high muscle mass may have a high BMI without excess body fat. Research also shows that people of Asian descent may face health risks at lower BMI thresholds. Always consult a healthcare provider for a complete health assessment that considers your full medical history.
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Health Tips
- →A BMI between 18.5 and 24.9 is considered healthy for most adults.
- →Regular physical activity and a balanced diet are the most effective ways to maintain a healthy BMI.
- →BMI is a screening tool — always consult a doctor for a full health assessment.
- →Muscle weighs more than fat — athletes may have a high BMI without health risks.
Estimate your body fat percentage using multiple methods.