Body Mass Index (BMI) is a simple screening measure that relates your weight to your height, giving a quick, standardized number that's widely used by health organizations as a starting point for assessing whether someone falls into an underweight, normal, overweight or obese range. This calculator accepts both metric (kilograms and centimetres) and imperial (pounds, feet and inches) units, so you don't need to convert anything manually.
It's worth remembering BMI doesn't distinguish between muscle and fat mass, so it's a general population-level indicator rather than a precise measure of individual body composition โ athletes and very muscular people, for example, can show a 'high' BMI despite low body fat.
In metric units: BMI = weight (kg) / height (m)ยฒ.
In imperial units: BMI = 703 ร weight (lb) / height (in)ยฒ.
The commonly used adult BMI categories are: below 18.5 = underweight, 18.5โ24.9 = normal weight, 25โ29.9 = overweight, and 30 and above = obese.
No single number can capture body composition perfectly. BMI doesn't account for muscle mass, bone density, age or sex, so it can misclassify very muscular people as 'overweight' and can be less reliable for older adults, athletes, pregnant women and children. It's best used as a general screening indicator, not a diagnosis.
For most adults, a BMI between 18.5 and 24.9 is generally categorized as the 'normal' or healthy weight range by major health organizations, though individual healthy ranges can vary by age, sex, ethnicity and muscle mass.
No โ BMI is a quick, free screening estimate, not a medical diagnosis. If you have concerns about your weight or health, a doctor or registered dietitian can assess body composition, health markers and risk factors far more accurately than BMI alone.