BMI Calculator

Use the free BMI Calculator to instantly find your Body Mass Index (BMI) and determine whether you are underweight, at a healthy weight, overweight, or obese. Supports both imperial (lb, ft+in) and metric (kg, cm) units with automatic category classification based on WHO standards.

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About the BMI Calculator

Your Body Mass Index (BMI) is a simple calculation that estimates your body fat level by comparing your weight to your height. It is widely used by health professionals as a quick screening tool for determining whether your weight falls within a healthy range.

Formula Used

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

BMI Categories (WHO Standard)

  • Underweight: BMI below 18.5
  • Normal weight: 18.5 – 24.9
  • Overweight: 25 – 29.9
  • Obese: 30 and above

Example Calculation

If you weigh 154 lb and are 5 ft 9 in (69 inches) tall:

BMI = 703 × 154 / (69 × 69) = 22.7 → Normal weight

How to Calculate BMI (Step-by-Step)

  1. Measure your height in centimeters or in feet + inches.
  2. Measure your weight in kilograms or pounds.
  3. Convert height:
    - Metric: cm → m (divide by 100)
    - Imperial: ft+in → inches
  4. Apply the correct BMI formula based on your unit system.
  5. Compare your result to the WHO BMI categories

Common Mistakes When Calculating BMI

  • Mixing up imperial and metric units
  • Entering height in feet but forgetting inches
  • Using centimeters directly without converting to meters
  • Confusing BMI with body fat percentage

Tips for Using This BMI Calculator

  • Metric (kg/cm) gives the most consistent results
  • Measure height without shoes
  • BMI is a screening tool — not a diagnosis
  • For body fat %, use the Body Fat Calculator

What BMI Does NOT Measure

BMI does not measure:

  • Body fat percentage
  • Muscle mass differences
  • Bone density
  • Fat distribution

Muscular individuals may appear “overweight” on the BMI scale despite having low body fat.