Calculate your Body Mass Index instantly using the WHO-standard formula. Free, accurate, and available in multiple languages.
Body Mass Index (BMI) is a numerical value calculated from your weight and height. Developed by Belgian mathematician Adolphe Quetelet in the 1830s, it is widely used by the World Health Organization (WHO) and healthcare professionals worldwide as a screening tool for weight-related health risks. According to WHO data, over 1.9 billion adults globally are overweight, with 650 million classified as obese - making BMI an important first-step assessment tool.
The BMI formula divides your weight in kilograms by the square of your height in meters: BMI = weight (kg) ÷ height² (m²). For example, a person weighing 70 kg with a height of 1.75 m has a BMI of 70 ÷ (1.75 × 1.75) = 22.9, which falls in the "Normal Weight" category. For imperial units, the formula is: BMI = (weight in pounds × 703) ÷ height² (in inches).
While BMI is a useful population-level screening tool, it has important limitations for individuals. It does not differentiate between muscle mass and fat mass - a muscular athlete may be classified as "overweight" despite having low body fat. BMI also does not account for fat distribution (visceral vs. subcutaneous fat), bone density, age-related changes, or ethnic variations in body composition. The WHO recommends using BMI alongside waist circumference and other clinical assessments for a comprehensive health evaluation.
| BMI | Category | Health Risk |
|---|---|---|
| 0 – 16 | Severe Underweight | High |
| 16 – 17 | Moderate Underweight | Moderate |
| 17 – 18.5 | Mild Underweight | Low-Moderate |
| 18.5 – 25 | Normal Weight | Low |
| 25 – 30 | Overweight | Moderate |
| 30 – 35 | Obese Class I | High |
| 35 – 40 | Obese Class II | Very High |
| 40+ | Obese Class III | Very High |