Number & Finance

BMI Calculator

Calculate Body Mass Index (BMI) for adults using metric or imperial units, categorised into standard health ranges.

How It Works & Methodology

Body Mass Index (BMI) is a simple index of weight-for-height that is commonly used to classify underweight, normal weight, overweight, and obesity in adult men and women. The World Health Organization (WHO) defines standard adult BMI thresholds.

Metric: BMI = weight (kg) / [height (m)]^2 Imperial: BMI = 703 * weight (lb) / [height (in)]^2 Standard Adult Cutoffs: < 18.5 Underweight, 18.5 – 24.9 Healthy range, 25.0 – 29.9 Overweight, ≥ 30.0 Obesity.
Key Assumptions & Scope:
  • Designed as a general screening tool for adult men and women aged 20 and older.
  • Does not differentiate between muscle mass and adipose tissue; may overestimate body fat in athletes.
  • Not suitable for diagnosing children, adolescents, pregnant individuals, or frail elderly persons.

Frequently Asked Questions

What is considered a healthy BMI for adults?

According to WHO and CDC guidelines, a BMI between 18.5 and 24.9 is considered within the healthy/normal weight range for adults.

Can BMI differentiate between muscle and fat?

No. BMI measures total body mass relative to height. Muscular athletes often have elevated BMIs that place them in the overweight category despite having low body fat percentages.

Does this calculator apply to children or teens?

No. Pediatric BMI assessments rely on age- and sex-specific percentile growth charts rather than fixed adult numerical thresholds.