One calculator, treated carefully. BMI is a screening number that public-health bodies use to talk about populations, and it is genuinely useful as a rough flag — but it is a ratio of weight to height and nothing more. It cannot tell muscle from fat, and it does not know where on your body the weight sits.
Which one do you want?
| If you are… | Use |
|---|---|
| A quick screening number in metric or US units | BMI Calculator — with the standard adult categories and the healthy weight range for your height. |
Categories follow the standard adult (20+) definitions used by the US Centers for Disease Control and Prevention. BMI is a screening tool, not a diagnosis: athletes with high muscle mass routinely read as "overweight", and it is not valid as-is for children, pregnancy, or the very elderly. Nothing here is medical advice — a doctor looking at you has information this number does not.
What BMI can and cannot tell you
- It measures a ratio, not body composition. BMI is weight divided by height squared. It cannot distinguish muscle from fat, which is why athletes with high lean mass routinely read as overweight while carrying very little body fat.
- It was designed to describe populations, not individuals. The formula comes from 19th-century work on population averages. It remains a useful screening figure across large groups and a blunt one for any single person.
- The standard categories do not apply to everyone. The adult thresholds are not valid as-is for children, during pregnancy, or for the very elderly, and research indicates the risk thresholds sit at different values across ethnic groups.
- Where fat sits matters more than how much. Waist circumference and waist-to-height ratio track metabolic risk more closely than BMI does, because abdominal fat behaves differently from fat elsewhere. A doctor looking at you has information this number does not.
Frequently asked questions
Is BMI accurate for me personally?
It is a population-level screening statistic. For an individual it is a starting point at best — waist circumference, body composition and family history all tell you things BMI cannot.
Why do athletes often show as overweight?
Muscle is denser than fat. BMI only knows your weight and height, so a muscular build and excess fat look identical to it.
Does BMI work for children?
Not with these adult categories. Children are assessed against age-and-sex percentile charts instead, which a paediatrician will use.