Calculate your Body Mass Index and understand your health category.
How the BMI Calculator Works
Body Mass Index (BMI) is a screening number calculated from your weight and height. It provides a quick, population-level estimate of whether a person falls into a weight range that is associated with increased health risks. BMI does not directly measure body fat, but research has shown it correlates well with more direct measures of body fat for most adults.
This calculator supports both metric units (kilograms and centimetres) and imperial units (pounds and inches). After entering your measurements, it instantly computes your BMI, classifies it into a WHO-defined category, and shows the healthy weight range for your height.
— your height in metres (metric) or inches (imperial); centimetres are divided by 100 before squaring
703
— the unit conversion factor used when weight is in pounds and height is in inches
Example Calculation
Suppose a person weighs 70 kg and is 175 cm (1.75 m) tall. Using the metric formula: BMI = 70 ÷ (1.75)² = 70 ÷ 3.0625 ≈ 22.9.
A BMI of 22.9 falls in the Normal weight range (18.5–24.9), which is associated with the lowest risk of weight-related health problems. For this person's height, the healthy weight range spans approximately 56.6 kg to 76.3 kg.
Frequently Asked Questions
For most adults aged 18–65, the World Health Organization defines a healthy BMI as 18.5 to 24.9. A BMI below 18.5 is classified as underweight, 25–29.9 as overweight, and 30 or above as obese. These thresholds are the same for both men and women, although body composition differences mean the categories are not equally predictive across sexes.
BMI can overestimate health risk for athletes and highly muscular individuals. Because muscle is denser than fat, a person with a large amount of lean muscle mass may have a high BMI despite having low body fat. In these cases, additional measures such as waist circumference or body fat percentage provide a more accurate health picture.
Standard BMI thresholds (18.5–24.9) are designed for adults only. For children and teenagers (ages 2–19), BMI is interpreted using age- and sex-specific percentile charts because normal amounts of body fat change with age and differ between boys and girls. A paediatrician should assess BMI in younger individuals.
Yes — BMI is a useful tracking metric when used alongside other indicators. Because it is calculated from weight and height alone, any change in weight directly changes your BMI, making it easy to monitor trends over time. However, also track waist measurement and energy levels to get a fuller picture of your health progress.
If you get a slightly different result between modes, it is most likely a rounding difference when converting between units. For best accuracy, use metric mode and enter your measurements directly in kilograms and centimetres, as the formula was originally defined using the metric system.