BMI Calculator Online Free

How to calculate BMI

Enter your height and weight. Body mass index is your weight in kilograms divided by the square of your height in metres, and the result is placed in one of the standard categories.

What the categories mean

The World Health Organization defines the ranges as: under 18.5 underweight, 18.5 to 24.9 normal, 25 to 29.9 overweight, and 30 or above obese. Several Asian health authorities, including in India, apply lower thresholds, overweight from 23 and obese from 25, because cardiometabolic risk in South Asian populations appears at lower BMI values.

What BMI cannot tell you

BMI was devised in the 1830s as a population statistic, not an individual diagnostic, and it has real limitations. It does not distinguish muscle from fat, so athletes are routinely classified as overweight while carrying very little fat. It says nothing about where fat is stored, though abdominal fat carries far more metabolic risk than fat elsewhere. That is why waist circumference and waist-to-height ratio are often more informative. It is unreliable for older adults, who lose muscle mass, and it is not valid at all for children, who are assessed against age-and-sex percentile charts instead.

Treat the number as one rough signal among several, alongside blood pressure, blood glucose, lipids, activity levels and how you actually feel.

Frequently asked questions

Is BMI useful at all, then?

At population scale, yes. It correlates well with health outcomes across large groups. It is the application to one individual that requires caution.

Which threshold should I use?

If you are of South Asian descent, the lower Asian cut-offs are the more relevant guidance. Your doctor can advise for your circumstances.

Is my data stored?

No. Height and weight are used for the calculation in your browser and never leave your device.

Is this medical advice?

No. This tool is for general information only and is not a diagnosis. Speak to a qualified healthcare professional about your health.