BMI Calculator
Body mass index, its band and the healthy range. Free, and runs entirely in your browser — nothing you enter is uploaded, stored or sent to a server.
About BMI Calculator
Body mass index is weight divided by height squared, and its whole value is that it is one number you can compare against a band. Under 18.5 is underweight, 18.5 to 24.9 is the healthy band, 25 to 29.9 is overweight, and 30 and above is obese in three classes.
The more useful output is the other direction: what the healthy band actually weighs at your height. That turns an abstract index into two numbers in kilograms, and says how far outside them you are if you are outside them.
Both unit systems are here because the question arrives in both: kilograms and centimetres, or pounds, feet and inches.
Where it helps
- Says what the healthy band weighs at your height, not just which band you are in.
- Handles metric and imperial without making you convert anything first.
- Shows the distance to the nearest edge of the healthy range in kilograms.
- Runs locally: height and weight are health data and they stay in the browser.
Limits
- BMI knows nothing about muscle: a trained athlete reads as overweight or obese on it.
- It also knows nothing about where weight is carried, and waist measurement predicts health risk better.
- The bands are drawn from adult populations and do not apply to children, or straightforwardly across every ethnicity.
- It is a screening number, not a diagnosis, and no single number replaces a doctor.
Frequently asked questions
Is BMI actually useful?
As a population screen, yes; as a verdict on one person, only roughly. It is a cheap first look that says whether a longer conversation is worth having.
Why does it read high for me?
Muscle is denser than fat, so a muscular build pushes the index up without any of the risk it is meant to flag. Waist-to-height ratio is a better check.
What is the healthy range at my height?
The result gives it in kilograms: it is 18.5 to 24.9 multiplied by your height in metres squared.
Does it apply to children?
No. Children are assessed on age-and-sex percentile charts, not against these adult bands.
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