How to Calculate BMI: Complete Guide to Body Mass Index
Learn how to calculate your Body Mass Index (BMI), understand what it means, and discover healthy weight ranges according to WHO standards.
What is BMI?
Body Mass Index (BMI) is a simple measurement that uses your height and weight to determine if your weight is healthy. It's used by healthcare professionals worldwide as a quick screening tool for weight categories that may lead to health problems.
The BMI Formula
BMI is calculated using this simple formula:
BMI = Weight (kg) ÷ Height (m)²
Or in imperial units: BMI = (Weight in lbs × 703) ÷ Height in inches²
Step-by-Step: How to Calculate Your BMI
Measure Your Weight
Weigh yourself in kilograms (kg). For best accuracy, weigh yourself in the morning before eating, wearing minimal clothing.
Measure Your Height
Measure your height in meters (m). Stand straight against a wall with your heels together and look straight ahead.
Square Your Height
Multiply your height by itself. For example, if you're 1.75m tall: 1.75 × 1.75 = 3.0625
Divide Weight by Height²
Divide your weight by your squared height. For example: 70kg ÷ 3.0625 = 22.86 BMI
BMI Categories (WHO Standards)
Once you've calculated your BMI, compare it to these categories established by the World Health Organization:
| Category | BMI Range | Health Risk |
|---|---|---|
| Underweight | Below 18.5 | Moderate |
| Normal weight | 18.5 – 24.9 | Low |
| Overweight | 25.0 – 29.9 | Increased |
| Obese Class I | 30.0 – 34.9 | High |
| Obese Class II | 35.0 – 39.9 | Very High |
| Obese Class III | 40.0 and above | Extremely High |
Limitations of BMI
While BMI is a useful screening tool, it has some limitations:
- Doesn't distinguish between muscle and fat mass
- May overestimate body fat in athletes
- May underestimate body fat in older adults
- Doesn't account for fat distribution
- Different cutoffs may apply for different ethnicities
Tips for Maintaining a Healthy BMI
- Balanced Diet: Eat a variety of fruits, vegetables, whole grains, and lean proteins.
- Regular Exercise: Aim for at least 150 minutes of moderate activity per week.
- Stay Hydrated: Drink plenty of water throughout the day.
- Get Enough Sleep: Poor sleep can affect weight management.
- Monitor Progress: Track your BMI regularly using our free calculator.