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What is BMI? Complete Guide to Body Mass Index Calculator

Learn everything about Body Mass Index (BMI), how to calculate it, what the results mean, and the limitations of using BMI as a health indicator.

2025-01-155 min

What is BMI?

Body Mass Index (BMI) is a simple calculation using a person's height and weight. The formula is BMI = kg/m² where kg is a person's weight in kilograms and m² is their height in meters squared.

How to Calculate BMI

The BMI formula is straightforward:

  • Metric: BMI = weight (kg) / height² (m²)
  • Imperial: BMI = (weight (lbs) × 703) / height² (inches²)

    • For example, a person weighing 70 kg and standing 1.75 m tall would have a BMI of: 70 / (1.75 × 1.75) = 22.9

    BMI Categories

    According to the World Health Organization (WHO), BMI categories are:

  • Underweight: Below 18.5
  • Normal weight: 18.5 – 24.9
  • Overweight: 25 – 29.9
  • Obesity Class I: 30 – 34.9
  • Obesity Class II: 35 – 39.9
  • Obesity Class III: 40 and above

    • Limitations of BMI

    While BMI is a useful screening tool, it has several limitations:

  • Doesn't distinguish fat from muscle: Athletes may have high BMI despite low body fat
  • Age considerations: Elderly individuals may have normal BMI but higher body fat
  • Ethnic variations: Asian populations may have higher health risks at lower BMI levels
  • No fat distribution info: BMI doesn't indicate where fat is stored

    • Why Use a BMI Calculator?

    Our free BMI calculator provides instant results and includes:

  • Both metric and imperial unit support
  • Visual classification of your result
  • Ideal weight range calculation
  • Health risk information

    • Understanding your BMI is the first step toward better health awareness.