BMI Calculator

BMI = weight (kg) / height (m)²

Health & Body

How to Use This Tool

What Is BMI?

Body Mass Index (BMI) is a screening tool that uses your height and weight to estimate body fat. It’s widely used by health organizations including the WHO and CDC to classify underweight, normal weight, overweight, and obese categories.

BMI Formula

Metric: BMI = weight (kg) / height (m)²

Imperial: BMI = 703 × weight (lb) / height (in)²

BMI Categories (WHO)

BMI Range Category
Below 18.5 Underweight
18.5 – 24.9 Normal weight
25.0 – 29.9 Overweight
30.0 and above Obese

Limitations of BMI

BMI is a useful screening tool but has known limitations:

  • It does not directly measure body fat.
  • Athletes with high muscle mass may have a high BMI without excess fat.
  • Older adults may have a higher body fat percentage at the same BMI as younger adults.
  • BMI does not account for fat distribution (visceral vs. subcutaneous fat).

Always consult a healthcare provider for personalized assessment.

Formula & Explanation

The BMI formula was developed by Adolphe Quetelet in the 1830s. The WHO established the current category thresholds in 1997 based on epidemiological data linking BMI to health outcomes.

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Frequently Asked Questions

What is a healthy BMI?

A BMI between 18.5 and 24.9 is considered healthy for most adults, according to the World Health Organization. Below 18.5 is underweight; 25-29.9 is overweight; 30+ is obese.

Is BMI accurate for athletes?

BMI can overestimate body fat in athletes and others with high muscle mass, because muscle is denser than fat. A muscular athlete may have a 'overweight' BMI despite low body fat. For athletic populations, body fat percentage measurements are more informative.

Does BMI work for children?

BMI for children (under 20) is calculated the same way but interpreted using age- and sex-specific percentile charts, not the adult categories. Consult a pediatrician for child BMI interpretation.

Is BMI the same as body fat percentage?

No. BMI is a height-weight ratio that estimates body fat indirectly. Body fat percentage measures actual fat mass directly (via DEXA, calipers, or bioimpedance). Two people with the same BMI can have very different body fat percentages.