Free BMI Calculator Online (Body Mass Index)

What Is BMI (Body Mass Index)?

Body Mass Index (BMI) is a simple weight-to-height ratio. Our free BMI calculator online helps you check your BMI instantly and compare it with standard BMI categories. While BMI is not a diagnosis, it can flag when a closer look is warranted—diet quality, activity level, and clinical markers like blood pressure and blood sugar.

How to Calculate BMI — Formula & Example

• Metric: BMI = weight (kg) ÷ [height (m)]²
• Imperial: BMI = (weight (lb) ÷ [height (in)]²) × 703

Adult BMI Chart & Categories

Why BMI Matters

As BMI rises, the statistical risk of certain conditions—like type 2 diabetes, high blood pressure, heart disease, sleep apnea, and fatty liver disease—tends to increase. Conversely, a very low BMI may be linked to nutrient deficiencies or other health issues.

Where BMI Falls Short

• It does not distinguish between muscle, bone, and fat mass.
• It doesn’t reflect fat distribution (e.g., abdominal vs. peripheral).
• It may misclassify athletes, older adults with sarcopenia, and individuals from different ethnic groups who face risk at different BMIs.

For a more complete assessment, consider waist circumference, body composition estimates, blood pressure, blood lipids, A1C/fasting glucose, and clinical history.

How to Improve or Maintain a Healthy BMI

1. Build balanced meals. Emphasize vegetables, fruits, legumes, whole grains, lean proteins, and healthy fats while limiting ultra-processed foods and added sugars.
2. Move regularly. Aim for at least 150 minutes of moderate activity weekly, plus 2+ days of resistance training.
3. Sleep & stress. Prioritize 7–9 hours of sleep and stress-management habits.
4. Track gently. Periodic check-ins with weight, waist size, and energy levels can guide adjustments.
5. Seek support. Dietitians, physicians, and structured programs can help with plateaus, medications, or surgical options where appropriate.

Frequently Asked Questions