BMI Calculator

According to the CDC, a BMI below 18.5 is considered underweight, 18.5–24.9 is normal (healthy) weight, 25.0–29.9 is overweight, and 30.0 or higher is obese. These categories apply to adults 20 and older.

BMI is calculated by dividing your weight in kilograms by the square of your height in meters: BMI = kg / m². In imperial units: BMI = (lbs / in²) × 703. For example, someone 5'9" (175cm) weighing 170 lbs has a BMI of 25.1.

BMI doesn't distinguish between fat mass and muscle mass, so athletes or muscular individuals may be classified as overweight despite having low body fat. It also doesn't account for age, sex, or ethnic differences in body composition. The CDC recommends using BMI alongside other assessments like waist circumference and body fat percentage.

The standard BMI formula is the same for both men and women, but body fat interpretation differs. Women naturally carry more body fat than men at the same BMI. For example, a BMI of 25 typically corresponds to about 33% body fat in women versus 22% in men (per NHLBI data). Some researchers advocate sex-specific cutoffs.

A BMI of 30.0 or higher is classified as obese by the CDC and WHO. Obesity is further divided into Class I (30–34.9), Class II (35–39.9), and Class III/severe obesity (40+). Studies show obesity significantly increases risk of heart disease, type 2 diabetes, and certain cancers.

For children ages 2–19, BMI is assessed using age- and sex-specific percentile charts. A child is underweight if below the 5th percentile, healthy weight at 5th–84th percentile, overweight at 85th–94th percentile, and obese at or above the 95th percentile. Source: CDC growth charts.