BMI Calculator
Calculate your Body Mass Index and find out if you're in a healthy weight range. Get personalized health recommendations based on your results.
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What is BMI?
Body Mass Index (BMI) is a numerical value derived from a person's weight and height. Developed by Adolphe Quetelet in the 1830s, BMI is used worldwide as a quick screening tool to categorize weight status.
Healthcare professionals use BMI to identify potential weight-related health risks. It is not a diagnostic tool — a high or low BMI indicates possible risk, but a doctor must evaluate overall health with additional tests.
How to Calculate BMI
Metric: BMI = weight (kg) ÷ height (m)²
Imperial: BMI = (weight (lbs) ÷ height (in)²) × 703
The constant 703 converts the imperial calculation to match the metric scale. For example, a person weighing 160 lbs at 5'7" (67 in): (160 ÷ 67²) × 703 = 25.1.
BMI Categories and Health Risks
| Category | BMI Range | Health Risk |
|---|---|---|
| 🔵 Underweight | < 18.5 | Nutritional deficiencies |
| 🟢 Normal | 18.5 – 24.9 | Low risk |
| 🟡 Overweight | 25.0 – 29.9 | Moderate risk |
| 🟠 Obese I | 30.0 – 34.9 | High risk |
| 🟠 Obese II | 35.0 – 39.9 | Very high risk |
| 🔴 Obese III | 40.0+ | Extremely high risk |
Limitations of BMI
BMI does not account for muscle mass, bone density, body composition, age, gender, or ethnicity. Athletes and bodybuilders often have high BMI despite low body fat.
BMI is less accurate for pregnant women, elderly individuals, and growing children. Alternative measures like body fat percentage, waist-to-hip ratio, and waist circumference can provide a more complete picture of health.
How to Achieve a Healthy Weight
• Balanced diet: Create a moderate calorie deficit (for weight loss) or surplus (for weight gain) with nutrient-dense foods.
• Regular exercise: Combine cardio (walking, running, cycling) with strength training for optimal body composition.
• Sleep & stress: Poor sleep and chronic stress contribute to weight gain. Aim for 7–9 hours of quality sleep.
• Gradual changes: Sustainable weight management comes from small, consistent lifestyle changes — not crash diets.
• Professional guidance: A registered dietitian or doctor can create a plan tailored to your specific needs.