How BMI is calculated
BMI divides weight in kilograms by height in metres, squared. It was designed in the 1830s as a population-level screening statistic — a quick way to flag people who might be carrying unusually low or high weight for their height, not a diagnostic measurement for any one individual.
A worked example
At 70 kg and 170 cm, BMI works out to 24.2 — inside the healthy 18.5–24.9 band, just under the overweight threshold. For that same height, the healthy weight range runs from about 53.5 kg to 72.0 kg.
Frequently asked questions
What counts as a healthy BMI?
The World Health Organization sets the healthy range at 18.5–24.9 for adults. Below that is classed as underweight, 25–29.9 as overweight, and 30 and above as obese. These thresholds apply to the general adult population and aren't adjusted for age or sex.
Why might BMI be misleading for me specifically?
BMI only uses height and weight — it can't tell the difference between muscle and fat. A muscular athlete and a sedentary person of the same height and weight get the same BMI, even though their actual body composition is very different. It's a useful population-level screening tool, not a precise individual diagnosis.
Does BMI work the same way for children?
No. Children and teens are assessed against age- and sex-specific growth charts, not the fixed adult thresholds used here. This calculator is intended for adults.
What should I do if my BMI is outside the healthy range?
Treat it as a starting point for a conversation, not a verdict. A doctor can factor in your waist circumference, body composition, and overall health to give context a BMI number alone can't provide.
This calculator is for general informational purposes only and is not a medical diagnosis. Talk to a doctor about what a healthy weight looks like for your individual circumstances.