BMI Calculator
Calculate your Body Mass Index (BMI) to determine if you are underweight, normal weight, overweight, or obese based on your height and weight.
Ages 2 - 120
What is BMI?
Body Mass Index (BMI) is a numerical value of your weight in relation to your height. It is a commonly used method to determine whether a person has a healthy body weight for their height. Specifically, the value obtained from the calculation of BMI is used to categorize whether a person is underweight, normal weight, overweight, or obese.
BMI is widely used as a risk factor for the development of or the prevalence of several health issues. It is used to broadly define different weight categories that may be associated with health problems, however, it is not an exact measurement of body fat or health.
How is BMI Calculated?
The BMI calculation formula is different depending on the unit system you use:
For the metric system (kilograms, meters), BMI is calculated by dividing weight in kilograms by the square of height in meters.
For the imperial system (pounds, inches), BMI is calculated by dividing weight in pounds by the square of height in inches, and then multiplying by a conversion factor of 703.
BMI Categories and Health Risk
| BMI Category | BMI Range (kg/m²) | Health Risk |
|---|---|---|
| Underweight | Below 18.5 | Malnutrition risk, decreased immune function, increased mortality |
| Normal Weight | 18.5 - 24.9 | Low risk (healthy range) |
| Overweight | 25.0 - 29.9 | Moderate risk of developing heart disease, high blood pressure, stroke, diabetes |
| Obesity Class I | 30.0 - 34.9 | High risk of developing heart disease, high blood pressure, stroke, diabetes |
| Obesity Class II | 35.0 - 39.9 | Very high risk of developing heart disease, high blood pressure, stroke, diabetes |
| Obesity Class III | 40.0 and above | Extremely high risk of developing heart disease, high blood pressure, stroke, diabetes |
Note: These BMI ranges are based on the relationship between body weight and disease and death. Overweight and obese individuals are at increased risk for many diseases and health conditions.
Limitations of BMI
While BMI is a useful measure of overall health for most people, it does have some limitations:
- BMI does not distinguish between weight from fat and weight from muscle, bone, or water. Athletes with high muscle mass may have a high BMI without excess fat.
- BMI may not be as accurate for older adults who have lost muscle mass.
- Ethnic differences in body composition may affect the interpretation of BMI. Different ethnic groups may have different associations between BMI and health risks.
- BMI is not applicable to pregnant or breastfeeding women.
- BMI does not account for the distribution of fat. Abdominal fat (visceral fat) carries higher health risks than fat in other areas.
Due to these limitations, BMI should be considered as one of several tools for assessing health, not the sole determinant.
How to Use This BMI Calculator
- Select your preferred units (metric or imperial).
- Enter your age and select your gender.
- Input your weight and height measurements accurately.
- Click the 'Calculate BMI' button to see your results.
For the most accurate assessment of your health status, consult with a healthcare professional who can consider additional factors beyond BMI.
Healthy Weight Management Tips
Balanced Diet
Focus on a variety of fruits, vegetables, whole grains, lean proteins, and healthy fats. Limit processed foods, added sugars, and excessive sodium.
Regular Physical Activity
Aim for at least 150 minutes of moderate-intensity activity or 75 minutes of vigorous activity per week, plus muscle-strengthening activities twice a week.
Healthy Habits
Get adequate sleep (7-9 hours for adults), manage stress, and stay hydrated. Avoid smoking and limit alcohol consumption.
Frequently Asked Questions
Is BMI the same for men and women?
Yes, the BMI calculation formula is the same for both men and women. However, the interpretation of BMI results can differ because women naturally have a higher percentage of body fat than men with the same BMI.
Is BMI accurate for athletes and bodybuilders?
BMI may overestimate body fat in athletes and others who have a muscular build. This is because muscle weighs more than fat, so someone with significant muscle mass might have a high BMI but not be overweight or obese.
How often should I check my BMI?
For most adults, checking BMI once or twice a year is sufficient, unless your healthcare provider recommends more frequent monitoring. Rapid changes in BMI may warrant medical attention.
Can children use this BMI calculator?
This calculator can be used for individuals aged 2 and older, but for children and teens (ages 2-19), BMI is age and sex-specific. Their results should be interpreted using growth charts and percentiles rather than the adult categories shown here.