Calculate your Body Mass Index and see where you fall on the weight scale
This Body Mass Index (BMI) calculator estimates your body fat based on height and weight. BMI is a simple screening tool that helps identify potential weight categories that may lead to health problems. While it does not directly measure body fat, it provides a useful starting point for assessing weight status. The calculator also computes BMI Prime and Ponderal Index for a more comprehensive assessment.
BMI is calculated by dividing your weight in kilograms by the square of your height in meters. For imperial measurements, the formula is BMI = (weight in lbs × 703) / height² (in²).
BMI Prime is the ratio of your BMI to the upper limit of the "normal" BMI range (25 kg/m²). A BMI Prime of 1.0 corresponds to a BMI of 25, which marks the boundary between normal and overweight. Values below 0.74 indicate underweight, 0.74–1.0 is normal, and above 1.0 is overweight. This dimensionless index makes it easy to compare across populations.
The Ponderal Index (also known as Rohrer's Index) is calculated as weight (kg) / height³ (m). It is similar to BMI but uses height cubed instead of squared, making it potentially more accurate for assessing body composition in taller or shorter individuals. It is sometimes preferred in pediatric and neonatal assessments.
For a given height, a healthy BMI of 18.5–25 kg/m² corresponds to a specific weight range. The calculator shows your estimated healthy weight range based on your height, helping you understand how your current weight compares to the recommended range.
The World Health Organization defines a BMI of 18.5–24.9 as normal weight. Below 18.5 is underweight, 25–29.9 is overweight, and 30 or above is obese. BMI Prime provides a quick check: below 0.74 is underweight, 0.74–1.0 is normal, above 1.0 is overweight.
The Ponderal Index (weight / height³) is an alternative to BMI that uses height cubed instead of squared. Research suggests it may better account for differences in body frame size and be more accurate for very tall or short individuals. A normal Ponderal Index ranges from roughly 11–14 kg/m³ for adults.
BMI may overestimate body fat in athletes and those with high muscle mass, since muscle weighs more than fat. For these individuals, body fat percentage measurements or waist-to-height ratio may provide a more accurate health assessment.
For children and teens aged 2–20, BMI is interpreted using age- and gender-specific percentiles rather than fixed cutoffs. A child's body fat changes with age and differs between boys and girls. Always consult a pediatrician or healthcare provider for accurate interpretation of BMI in children.