Health & Body Composition
BMI Calculator
Type your numbers and get your full body-mass profile instantly, category, health risk, healthy weight range, and BMI Prime. No button. No waiting.
BMI (Body Mass Index) is a screening measure of body fat calculated from weight and height: weight in kilograms divided by height in meters squared. A BMI of 18.5–24.9 is considered healthy for most adults; 25–29.9 indicates overweight, and 30 or above indicates obesity.
Healthy BMI: 18.5–24.9 for most adults.
Formula: weight (kg) ÷ height² (m²).
Limit: a screening tool, not a body-fat measure or diagnosis.
Calculate Your BMI
Your Body Mass Index
What Is BMI?
The Body Mass Index (BMI) is a weight-to-height screening measure. It doesn't directly measure body fat or diagnose health, but it can help identify weight categories that may warrant discussion with a healthcare professional.
First described by the Belgian statistician Adolphe Quetelet in the 1830s, BMI was later adopted by the World Health Organization and the CDC as a standard population screening measure.
How It Is Calculated
Metric: BMI = weight (kg) ÷ height² (m²)
Imperial: BMI = [weight (lbs) ÷ height² (in²)] × 703
Example: Example: 70 kg ÷ (1.75 m × 1.75 m) = BMI 22.9 → Healthy Weight
Adult BMI categories (WHO/NIH)
| BMI Range | Weight Category | Health Risk |
|---|---|---|
| Below 18.5 | Underweight | Increased risk of nutritional deficiencies and osteoporosis |
| 18.5–24.9 | Normal Weight | Lowest health risk, maintain this range |
| 25.0–29.9 | Overweight | Increased risk of weight-related conditions |
| 30.0 and above | Obese | High risk of serious health conditions |
BMI compared with Waist-to-Height Ratio (WHtR)
| Data point | BMI | Waist-to-Height Ratio (WHtR) |
|---|---|---|
| What it measures | Weight relative to height | Central (abdominal) fat distribution |
| Inputs needed | Weight + height | Waist circumference + height |
| Healthy range (adults) | 18.5–24.9 | 0.50 or less |
| Strengths | Simple, well-studied, universal thresholds | Better cardiovascular-risk predictor; works for muscular builds |
| Limitations | Can't distinguish fat from muscle; ignores fat distribution | Depends on accurate waist measurement technique |
| Best for | Population screening, quick tracking | Individual cardiometabolic risk |
Limitations
- Muscle mass: athletes may have a high BMI with low body fat.
- Age: adult ranges don't apply to children or teens (they need BMI-for-age percentiles).
- Body composition: BMI doesn't distinguish fat, muscle, and bone.
- Ethnicity: some groups face higher risk at the same BMI.
- Pregnancy: not applicable during pregnancy.
Sources & Review
References used for this calculator’s formulas and thresholds:
BMI FAQ
What is a healthy BMI range?
A healthy BMI range for most adults is 18.5 to 24.9, which is associated with the lowest risk of weight-related health problems. Individual factors such as muscle mass, age, and ethnicity should also be considered.
How accurate is BMI for measuring health?
BMI is a useful screening tool but not a diagnostic measure of health. It provides a general indication of weight-related risk but doesn't account for muscle mass, bone density, or fat distribution.
Should children use the same BMI calculator?
No. Children and teens need age- and sex-specific BMI-for-age percentiles because their body composition changes with growth. Adult BMI categories don't apply to people under 20 years old.
What is BMI Prime?
BMI Prime is your BMI divided by 25, the top of the healthy range. A value below 1.00 sits inside the healthy range, and a value above 1.00 sits above it.
Important disclaimer: Results are educational estimates, not a substitute for professional medical advice. Discuss your numbers with a clinician before acting on them.