BMI Calculator

Calculate your Body Mass Index (BMI) and get personalized health insights based on your height and weight.

🧮 Use the BMI Calculator

What is BMI?

Body Mass Index (BMI) is a widely used screening tool that estimates body fat based on your weight and height. It provides a simple numeric measure that helps categorize individuals as underweight, normal weight, overweight, or obese.

The BMI formula was developed in the 1830s by Belgian mathematician Adolphe Quetelet. While it doesn't directly measure body fat percentage, research shows it correlates reasonably well with more direct measures of body fat for most people.

Health organizations worldwide, including the CDC, WHO, American Heart Association, and National Heart, Lung, and Blood Institute, use BMI as a first-line assessment tool for weight-related health risks. However, it's important to remember that BMI is just one indicator and should be considered alongside other health metrics.

How to Use This Calculator

Choose your preferred unit system (US Units or Metric Units) using the tabs at the top.
Enter your age (between 2 and 120 years). Note: For children and teens under 20, BMI should be interpreted using age- and sex-specific percentile charts.
Select your gender. While BMI calculation is the same for both sexes, health implications may differ.
Enter your height. For US Units, input feet and inches separately. For Metric Units, enter your height in centimeters.
Enter your weight in pounds (US Units) or kilograms (Metric Units), then click 'Calculate BMI' to see your results.

Latest Research & Insights

BMI as a Screening Tool

BMI is endorsed by major health agencies as a reliable population-level and first-line individual screening measure. The CDC, American Heart Association, NHLBI, and American Cancer Society all recognize BMI as a useful tool for identifying potential weight-related health risks, though they emphasize it should not be the sole determinant of health status.

Associated Health Risks

Research consistently shows that BMI correlates with risks for cardiometabolic diseases and mortality. High BMI is associated with increased risk of heart disease, type 2 diabetes, certain cancers, sleep apnea, and other chronic conditions. Conversely, very low BMI can indicate malnutrition or other health concerns.

Current Guidelines

For most adults, a healthy weight is defined as BMI 18.5–24.9. Overweight is classified as BMI 25.0–29.9, while obesity begins at BMI ≥30 and is often subdivided into Class I (30–34.9), Class II (35–39.9), and Class III (≥40). These categories help healthcare providers assess health risks and recommend appropriate interventions.

Important Limitations

Contemporary research emphasizes that BMI is convenient but imperfect. It does not directly measure body fat or its distribution, and cannot distinguish fat from muscle or bone mass. BMI may be less accurate for older adults, very muscular individuals (such as athletes), people at extremes of height, and may perform differently across racial and ethnic groups. For this reason, experts recommend using BMI together with other measures such as waist circumference, waist-to-height ratio, blood pressure, lipids, and blood glucose.

Best Practices

Use accurate measurements: measure height without shoes and current body weight on a calibrated scale.
Interpret BMI as a screening result, not a diagnosis. A high or low BMI should prompt discussion with a healthcare professional.
Consider individual context: BMI standards for adults don't apply to children/teens (who need age-specific percentiles), very muscular individuals, or older adults.
Combine BMI with other health metrics: waist circumference, blood pressure, cholesterol, blood glucose, physical activity level, and overall lifestyle factors provide a more complete picture of health.

Understanding BMI in Detail

The BMI Formula

BMI is calculated by dividing your weight in kilograms by the square of your height in meters: BMI = weight (kg) / height (m)². For imperial units, the formula is: BMI = (weight in pounds × 703) / (height in inches)². This calculator handles both unit systems automatically.

BMI Categories for Adults

Severe Thinness: BMI < 16
Moderate Thinness: BMI 16.0–16.9
Mild Thinness: BMI 17.0–18.4
Normal/Healthy Weight: BMI 18.5–24.9
Overweight: BMI 25.0–29.9
Obese Class I: BMI 30.0–34.9
Obese Class II and III: BMI ≥35.0

Additional Metrics

This calculator also provides BMI Prime (your BMI divided by 25, the upper limit of normal BMI) and Ponderal Index (weight divided by height cubed), which can offer additional context. A BMI Prime of 1.0 means you're at the upper boundary of healthy weight, while values above 1.0 indicate overweight or obesity.

Frequently Asked Questions

Is BMI accurate for everyone?

BMI is a useful screening tool for most adults, but it has limitations. It may overestimate body fat in athletes and muscular individuals, and underestimate it in older adults who have lost muscle mass. It also doesn't account for fat distribution, which is important for health risk assessment. For the most accurate health evaluation, BMI should be used alongside other measures like waist circumference and clinical assessments.

Can I use this calculator for children?

While you can calculate BMI for children using this tool, the interpretation is different. For children and teens aged 2-19, BMI must be compared to age- and sex-specific growth charts to determine percentiles. A BMI that's healthy for an adult might not be appropriate for a child. Consult your pediatrician for proper interpretation of children's BMI.

What should I do if my BMI is outside the healthy range?

If your BMI is below 18.5 or above 25, consider consulting with a healthcare provider. They can assess your overall health, review other risk factors, and provide personalized recommendations. Remember that BMI is just one indicator—your doctor will consider your complete health picture, including medical history, lifestyle, and other measurements.

How often should I check my BMI?

For most people, checking BMI every few months is sufficient to track long-term trends. If you're actively working on weight management, monthly checks can help monitor progress. However, don't obsess over small daily fluctuations—weight naturally varies due to hydration, meals, and other factors. Focus on long-term trends rather than day-to-day changes.

Does muscle weigh more than fat?

Muscle is denser than fat, meaning it takes up less space for the same weight. This is why very muscular individuals may have a high BMI despite having low body fat. If you're strength training and building muscle, your BMI might increase even as you become healthier and leaner. This is one reason why BMI should be considered alongside other measures like waist circumference and body composition.

What's the difference between BMI and body fat percentage?

BMI is an indirect estimate based on height and weight, while body fat percentage directly measures the proportion of your body that's fat versus lean mass (muscle, bone, organs). Body fat percentage is more accurate but requires specialized equipment like DEXA scans, bioelectrical impedance, or skinfold calipers. BMI is simpler and more accessible, making it useful for screening, but it doesn't tell you exactly how much fat you have or where it's located.