BMI Calculator: What Is BMI and How to Calculate It Correctly

What Is BMI?

Body Mass Index (BMI) is a numerical value calculated from a person's weight and height. It's the most widely used screening tool for classifying body weight relative to height. BMI was developed by Adolphe Quetelet in the 1830s and adopted by the World Health Organization as a standard health indicator.

The BMI Formula

BMI = weight (kg) / height² (m)

// Or in Imperial units:
BMI = (weight (lbs) × 703) / height² (inches)

BMI Categories (WHO Standard)

BMI Range	Category	Health Risk
Below 18.5	Underweight	Nutritional deficiency, osteoporosis
18.5 – 24.9	Normal weight	Lowest risk
25.0 – 29.9	Overweight	Moderate risk
30.0 – 34.9	Obese (Class I)	High risk
35.0 – 39.9	Obese (Class II)	Very high risk
40.0 and above	Severely obese (Class III)	Extremely high risk

Limitations of BMI

BMI is a useful population-level screening tool but has known limitations for individuals:

• ⚠️ Muscle vs. fat — Athletes with high muscle mass may have a high BMI despite low body fat.
• ⚠️ Age — BMI doesn't account for muscle loss with age (sarcopenia).
• ⚠️ Sex differences — Women typically have more body fat than men at the same BMI.
• ⚠️ Ethnicity — WHO has different BMI thresholds for Asian populations (overweight: 23+).
• ⚠️ Fat distribution — Abdominal fat is more dangerous than peripheral fat, which BMI doesn't measure.

Better Health Metrics to Use Alongside BMI

• Waist circumference — Men: <94 cm, Women: <80 cm for low risk.
• Waist-to-hip ratio — More accurate predictor of cardiovascular risk.
• Body fat percentage — Use FavorTool Body Fat Calculator.
• DEXA scan — Most accurate body composition measurement.

Calculate Your BMI Now

Use FavorTool BMI Calculator to instantly calculate your BMI in both metric (kg/cm) and imperial (lbs/in) units. The results include your BMI category, a visual range indicator, and personalized interpretation.