The Body Mass Index (BMI) Calculator is a widely used health screening tool that estimates body fat based on your height and weight. BMI provides a simple numeric value that categorizes you as underweight, normal weight, overweight, or obese, helping you and your healthcare provider assess potential health risks.
BMI was devised by Belgian mathematician Adolphe Quetelet in the 1830s and has been used by the World Health Organization (WHO) since the 1980s as the standard for recording obesity statistics. While it does not directly measure body fat percentage, it correlates well with more direct measures of body fat such as underwater weighing and dual-energy X-ray absorptiometry (DEXA).
Healthcare providers use BMI as a first-step screening tool. A BMI outside the normal range may prompt further assessments such as skinfold thickness measurements, diet evaluation, physical activity level assessment, and family health history reviews.
How the Formula Works
BMI = Weight (kg) ÷ Height (m)². For imperial units: BMI = (Weight in lbs × 703) ÷ (Height in inches)².
Metric: BMI = weight in kilograms ÷ (height in meters)²
Imperial: BMI = (weight in pounds × 703) ÷ (height in inches)²
Example: 70 kg ÷ (1.75 m)² = 70 ÷ 3.0625 = 22.86
How to Use This Calculator
Select your preferred unit system (Metric or Imperial)
Enter your weight in kilograms or pounds
Enter your height in centimeters or feet and inches
Click Calculate to see your BMI value and category
Review the BMI chart below to understand your health range
Tips & Best Practices
BMI is a screening tool, not a diagnostic tool — always consult a healthcare provider for a complete health assessment
Measure your height and weight at the same time of day for consistency
For children and teens (ages 2–20), BMI is interpreted using age- and sex-specific percentile charts
Athletes may have a high BMI due to muscle mass, not excess fat
Important Limitations
Does not distinguish between muscle mass and fat mass — muscular athletes may be classified as overweight
Does not account for age, sex, ethnicity, or body composition differences
May underestimate body fat in older adults who have lost muscle mass
Not applicable to pregnant or breastfeeding women
Does not indicate where fat is distributed (abdominal fat is more dangerous than fat on hips/thighs)
Different ethnic groups may have different health risk thresholds — WHO suggests lower cutoffs for Asian populations (overweight at BMI ≥ 23)