BMI calculator
Calculate your BMI
Body Mass Index
- Body Mass Index (BMI)—
- BMI Category—
- Healthy BMI range18.5 – 25 kg/m²
- Healthy weight for the height—
- Gain to reach BMI 18.5—
- Lose to reach BMI 25—
- Ponderal Index—
The free Body Mass Index (BMI) calculator estimates and categorizes BMI for both adults and children, based on the official growth and weight standards provided by the World Health Organization (WHO) and the Centers for Disease Control and Prevention (CDC).
What Is BMI (Body Mass Index)?
Body Mass Index (BMI) is a simple screening measure that relates your weight to your height to estimate whether you are underweight, within a healthy weight range, overweight, or have obesity. It’s widely used by public-health organizations as an initial risk indicator for weight-related conditions. Source: CDC
BMI Formulas
Metric formula
BMI = weight (kg) ÷ [height (m)]2
US/Imperial formula
BMI = weight (lb) ÷ [height (in)]2 × 703
These definitions and conversion factors are consistent with guidance from national health bodies. Source: NHLBI (NIH) | Source: NHS
Example Calculations
- Metric: 80 kg and 1.80 m → BMI = 80 ÷ (1.80 × 1.80) = 80 ÷ 3.24 ≈ 24.7
- US: 176.4 lb and 70 in → BMI = 176.4 ÷ (70 × 70) × 703 = 176.4 ÷ 4900 × 703 ≈ 25.3
Adult BMI Categories
Commonly used BMI ranges for adults (age ≥ 20):
| Category | BMI (kg/m²) |
|---|---|
| Underweight | < 18.5 |
| Healthy weight | 18.5–24.9 |
| Overweight | 25.0–29.9 |
| Obesity | ≥ 30.0 |
Ranges are aligned with public health guidance. Source: CDC
What BMI Can and Can’t Tell You
- Useful as a quick screen: Higher BMI is associated with increased risk of type 2 diabetes, heart disease, hypertension, and certain cancers. NHLBI
- Limitations: BMI doesn’t distinguish fat from muscle or reflect fat distribution; athletes may have “high” BMI but low body fat. Consider waist circumference and clinical assessment alongside BMI. CDC
- Populations & age: Cut-offs are for adults; for children/teens, BMI is age- and sex-specific (BMI-for-age percentiles). CDC
How to Use the BMI Calculator
- Select US (ft/in, lb) or Metric (cm, kg).
- Enter your age, height, and weight.
- Click Calculate to see your BMI, category, healthy weight range for your height, and Ponderal Index.
- Use the results as a starting point and discuss any concerns with a qualified healthcare professional.
Conversions You May Need
- inches → meters: in × 0.0254 = m
- centimeters → meters: cm ÷ 100 = m
- pounds → kilograms: lb × 0.45359237 = kg
References
- Centers for Disease Control and Prevention (CDC): About Adult BMI
- National Heart, Lung, and Blood Institute (NHLBI): Calculate Your BMI
- NHS (UK): BMI Healthy Weight Calculator
Disclaimer: BMI is a general screening tool and not a diagnostic measure. Always consult a healthcare professional for personalized advice.
