Where your weight actually sits.

What BMI measures, and what it does not

BMI is a ratio of weight to height squared. It was designed as a population screening tool in the 1830s, and it is used individually today mainly because it is cheap. Knowing its limits makes the number more useful, not less.

1. Enter your height and weight. Metric or imperial, whichever you know. The unit toggle converts the values you have already typed rather than clearing them, so switching does not mean starting again.
2. Read the number and the band. The result places you in one of the standard categories. Those thresholds come from the World Health Organization and are the ones most health services use.
3. Look at the healthy weight range. This is often more useful than the BMI itself: it tells you the weight band that would put you in the middle category at your height, which is a concrete target rather than an abstract score.
4. Treat it as one input. BMI cannot tell muscle from fat, cannot see where fat is stored, and was not designed for individuals. It is a starting point for a conversation, not a diagnosis.

When this comes up

• A rough check before a doctor’s appointment. Useful context for a conversation, not a substitute for one.
• Tracking a direction over time. BMI’s real strength is comparability: the same person at two points in time, measured the same way, shows a trend that is meaningful even if the absolute number is imperfect.
• Understanding a threshold in a medical form. Insurance questionnaires and some clinical guidelines still use BMI bands, so knowing where you sit explains the questions being asked.
• Sanity-checking a weight goal. The healthy range at your height is a more grounded target than a number picked from a magazine.

Questions