How to Calculate BMI: Formula, Chart & Free Online Calculator

What Is BMI?

Body Mass Index (BMI) is a numerical value calculated from your height and weight. It provides a quick screening method to categorize individuals into weight categories — underweight, normal weight, overweight, and obese. BMI is widely used by healthcare professionals as an initial assessment tool.

While BMI is not a perfect measure of health (it does not distinguish between muscle and fat), it remains one of the most accessible and widely referenced health metrics worldwide.

The BMI Formula

Metric Formula

BMI = weight (kg) / height (m)²

For example, a person weighing 70 kg who is 1.75 m tall:

BMI = 70 / (1.75 × 1.75) = 70 / 3.0625 = 22.86

Imperial Formula

BMI = (weight (lbs) × 703) / height (inches)²

For example, a person weighing 155 lbs who is 5 feet 9 inches (69 inches) tall:

BMI = (155 × 703) / (69 × 69) = 108,965 / 4,761 = 22.89

Skip the math — use our free BMI Calculator for instant results.

BMI Categories

World Health Organization (WHO) Classification

What Your BMI Score Means

Your BMI provides a general indication of whether your weight is within a healthy range for your height. It is a starting point for health conversations, not a definitive diagnosis.

Limitations of BMI

Does Not Measure Body Composition

BMI cannot distinguish between muscle, fat, bone, and water. A muscular athlete and a sedentary person of the same height and weight will have identical BMI scores, even though their body compositions are very different.

Age and Gender Differences

BMI does not account for natural differences in body composition between men and women, or changes that occur with aging.

Ethnic Variations

Research shows that health risks associated with specific BMI values can vary among different ethnic groups. For example, some Asian populations may face increased health risks at lower BMI thresholds.

Not Suitable for Everyone

BMI may not be accurate for:

Complementary Health Metrics

Waist Circumference

Measures abdominal fat, which is more closely linked to health risks than overall weight. A waist circumference above 40 inches for men or 35 inches for women indicates increased risk.

Waist-to-Hip Ratio

Divides your waist measurement by your hip measurement. A ratio above 0.90 for men or 0.85 for women suggests higher health risk.

Body Fat Percentage

Directly measures the proportion of fat in your body. More accurate than BMI but requires specialized equipment (calipers, bioelectric impedance, DEXA scan).

Healthy Weight Management Tips

Focus on Sustainable Habits

Rather than crash diets or extreme exercise programs, focus on small, sustainable changes:

Track Progress Beyond the Scale

Weight fluctuates daily due to water retention, food intake, and other factors. Track trends over weeks and months, not day-to-day changes. Consider tracking energy levels, fitness performance, and how your clothes fit in addition to weight.

Consult a Professional

BMI is a screening tool, not a diagnosis. For personalized health advice, consult a healthcare professional who can consider your complete health picture.

Free Health and Calculator Tools

Conclusion

BMI is a useful starting point for understanding your weight relative to your height, but it has limitations. Use our free BMI Calculator for a quick calculation, and consider complementary metrics like waist circumference and body fat percentage for a more complete picture. For personalized health guidance, always consult a healthcare professional.