What is BMI?
Body Mass Index (BMI) is a value calculated from a person's weight and height. It provides a simple numeric measure that can be used to categorize people as underweight, normal weight, overweight, or obese.
How is BMI Calculated?
In metric units: BMI = weight (kg) ÷ height² (m). In imperial units: BMI = 703 × weight (lbs) ÷ height² (inches).
BMI Categories
Below 18.5 is underweight. 18.5–24.9 is normal weight. 25–29.9 is overweight. 30 and above is obese. These categories apply to adults 20 years and older.
Limitations of BMI
BMI doesn't account for muscle mass, bone density, age, or sex. Athletes often have a "high" BMI despite being very healthy, while older adults may have a "normal" BMI with dangerous levels of body fat.
Using Our BMI Calculator
Our free BMI Calculator supports both metric and imperial units and shows your healthy weight range. Remember to treat it as a screening tool, not a diagnosis.