Maintaining a healthy weight is one of the most important aspects of long-term cardiovascular and metabolic wellness. To help assess whether your current weight is in a healthy proportion to your height, health organizations around the world use the Body Mass Index (BMI). This simple mathematical index acts as an initial screening tool for adult weight categories.
Body Mass Index is a value derived from the mass (weight) and height of an individual. The mathematical formula defines BMI as body weight in kilograms divided by the square of body height in meters:
BMI = Weight (kg) / [Height (m)]²
If you are using imperial measurements (pounds and inches), the formula requires a scaling conversion factor to align with metric standards:
BMI = [Weight (lb) / [Height (in)]²] × 703
To plan your target daily calorie needs based on your body mass, try our daily calorie estimator. For checking raw body fat percentage from waist measurements, visit our body fat percentage calculator.
For adults aged 20 and older, BMI values are grouped into standard categories defined by the World Health Organization (WHO): - Underweight: BMI below 18.5 - Normal Weight: BMI between 18.5 and 24.9 - Overweight: BMI between 25.0 and 29.9 - Obese: BMI of 30.0 or higher
A healthy weight range for an adult is calculated to keep their BMI between 18.5 and 24.9, which is associated with lower health risks. To translate weight or height measurements across different unit systems, visit our standard measurement conversions tool.
While BMI is a useful screening tool, it has limitations because it does not directly measure body fat.
Because it only considers height and weight, it cannot distinguish between bone, muscle mass, and fat. Therefore, highly active individuals, athletes, or bodybuilders with large amounts of muscle mass may be classified as "overweight" or "obese" despite having very healthy levels of body fat. Conversely, elderly individuals who have lost muscle mass may fall into the "normal" range despite having excess fat.
Additionally, standard BMI scales do not account for fat distribution. Abdominal fat (visceral fat) is associated with higher risks of cardiovascular disease and type 2 diabetes than subcutaneous fat stored in other areas like the hips. Therefore, someone with a normal BMI but high abdominal fat may still face elevated metabolic health risks.
To analyze these weight categories as ratios, try our relative ratio solver. To verify average body weights across multiple demographic samples, try our group average finder.
Suppose an adult is 1.75 meters tall and weighs 70 kilograms.
First, square the height in meters: - 1.75 × 1.75 = 3.0625.
Next, divide the weight by this squared height: - BMI = 70 / 3.0625 ≈ 22.86.
Since 22.86 falls between 18.5 and 24.9, this individual is in the Normal Weight category. To check standard math operations, use our everyday daily math helper.