BMI Calculator
Calculate your BMI (Body Mass Index) instantly. Supports imperial (ft, lbs) and metric (cm, kg). Shows BMI category — underweight, normal, overweight, or obese.
Reviewed for accuracy by Marcus Webb and the Blueprint Dynamics editorial team (last updated July 2026). Our calculators use primary-source formulas and are cross-checked against IRS publications, Fannie Mae guidelines, and Federal Reserve data. Learn more about our methodology.
Your BMI
25.8
Overweight
Underweight
< 18.5
Normal weight
18.5 – 24.9
Overweight
25 – 29.9
Obese
≥ 30
What BMI is and how to calculate it
Body Mass Index (BMI) is a simple screening number calculated by dividing your weight in kilograms by the square of your height in meters: BMI = kg/m². In imperial units, the formula is (weight in pounds × 703) divided by (height in inches)². For a 5'8" (68 inches) person weighing 160 lbs: BMI = (160 × 703) / (68²) = 112,480 / 4,624 = 24.3. This calculator does the conversion automatically — enter your measurements in whichever unit system you prefer.
BMI categories for adults
The CDC and World Health Organization use the same four adult categories: Underweight (BMI below 18.5), Normal weight (18.5–24.9), Overweight (25.0–29.9), and Obese (30.0 and above). Obesity is further subdivided: Class I (30–34.9), Class II (35–39.9), and Class III — sometimes called severe or morbid obesity (40 and above). These cutoffs are the same for all adults regardless of age or sex, though separate BMI-for-age charts apply to children and teens.
What BMI tells you — and what it doesn't
BMI correlates reasonably well with body fat percentage at the population level, which is why it's used in large health studies and screening programs. But it has well-documented limitations at the individual level. It cannot distinguish between fat mass and lean mass — a highly muscular person with 10% body fat may have a BMI in the "overweight" range. Conversely, an older adult who has lost muscle (sarcopenia) may have a "normal" BMI while carrying a high proportion of body fat.
Research consistently shows that waist circumference and waist-to-height ratio are stronger predictors of cardiovascular disease risk than BMI, because abdominal fat (visceral fat surrounding internal organs) drives metabolic risk more than overall body weight. A healthy waist circumference is generally under 35 inches for women and under 40 inches for men.
BMI and health risk
While imperfect, BMI does correlate with health outcomes at the population level. Sustained BMI above 30 is associated with increased risk of type 2 diabetes, hypertension, sleep apnea, certain cancers, and cardiovascular disease. BMI below 18.5 is associated with bone density loss, immune deficiency, and nutrient deficiencies. The lowest all-cause mortality in large longitudinal studies is found at BMIs of approximately 22–24.
Ethnicity also affects the relationship between BMI and health risk. Research shows that people of Asian descent have higher metabolic risk at lower BMI values — the World Health Organization and several Asian health organizations use lower cutoffs (overweight at 23, obese at 27.5) for these populations.
Using BMI alongside other measures
Think of BMI as one data point among several. For a fuller picture, consider tracking: waist circumference, waist-to-hip ratio, resting heart rate, blood pressure, fasting blood glucose, and HbA1c. Body fat percentage measured by DEXA scan (most accurate), hydrostatic weighing, or air displacement plethysmography gives a direct measure of fat vs. lean mass that BMI cannot provide. If your BMI is at a borderline value, these additional measures help clarify whether intervention is warranted. Always discuss results with a qualified healthcare provider.