Health
BMI Calculator
Calculate your Body Mass Index (BMI) in metric or imperial units. Get your BMI category, ideal weight range, and health risk assessment. Free, instant results.
Understanding BMI
BMI is a standardized measure of weight-to-height ratio, widely used by healthcare providers as a screening tool. While not perfect, BMI correlates with body fat and health risks for most people. Use it as one indicator alongside other health metrics.
How BMI Is Calculated
Metric formula
BMI = weight in kilograms divided by height in meters squared: kg / m². This calculator takes your height in centimeters and converts it to meters before applying the formula, then rounds the result to one decimal place.
Imperial formula
For pounds and feet/inches, the tool first converts weight to kilograms (multiplying by 0.453592) and height to meters (feet and inches combined, then multiplied by 0.0254), so the underlying calculation is always the same metric formula. This avoids the common imperial shortcut of multiplying by 703, though the two methods produce equivalent results.
Ideal weight range
The ideal weight range shown is the weight that would put you at the boundaries of the normal category, calculated as 18.5 × height² (minimum) and 24.9 × height² (maximum). It scales with your actual height, so taller and shorter people get different target ranges.
BMI Categories Explained
Underweight: below 18.5
May indicate a nutritional deficiency or increased osteoporosis risk. Consider consulting a healthcare provider if this is unintentional.
Normal weight: 18.5 to 24.9
Associated with the lowest average health risk in most population studies. This is the range the "ideal weight" box targets.
Overweight: 25 to 29.9
Linked to increased risk of cardiovascular disease and type 2 diabetes. Small, sustained changes in diet and activity typically move BMI back toward normal.
Obese Class I: 30 to 34.9
High risk of cardiovascular disease and diabetes. Clinical guidelines generally recommend structured weight management at this stage.
Obese Class II: 35 to 39.9
Very high risk of related health problems. Medical supervision is commonly recommended for weight management planning.
Obese Class III: 40 and above
Extremely high risk category, sometimes called severe or morbid obesity in clinical literature. Consult a healthcare provider for a full assessment.
Common Use Cases
Limitations to Keep in Mind
BMI only uses weight and height, so it cannot distinguish muscle mass from fat mass and does not account for where fat is stored on the body.
- Athletes and highly muscular people may show as overweight or obese despite low body fat.
- Older adults can lose muscle mass, so a "normal" BMI may still mask a high body fat percentage.
- Fat distribution (waist circumference and waist-to-hip ratio) is a stronger predictor of cardiovascular risk than BMI alone.
How this is calculated
Method: Body Mass Index, weight in kilograms divided by height in meters squared
BMI is your weight in kilograms divided by the square of your height in meters. With imperial units the same figure comes from weight in pounds divided by height in inches squared, multiplied by 703.
The result is classified using the standard World Health Organization ranges: below 18.5 is underweight, 18.5 to 24.9 is a healthy weight, 25 to 29.9 is overweight, and 30 or above is obese. BMI is a population-level screening measure. It does not distinguish muscle from fat, so very muscular people can read as overweight despite low body fat.
Sources and references
- World Health Organization, Obesity and overweight (fact sheet)
- Centers for Disease Control and Prevention, About BMI
This tool provides estimates for general information only, not professional advice. See our Disclaimer. Last reviewed: July 2026.