BMI Calculator

The BMI Calculator works out your Body Mass Index, a single number that relates your weight to your height and places you in a broad weight category. You enter your height and weight, choose metric (centimeters and kilograms) or imperial (feet, inches and pounds), and the tool applies the standard formula: weight in kilograms divided by height in meters squared. When you use imperial units it converts your figures first, so a 5-foot-9, 165-pound entry becomes roughly 1.753 meters and 74.8 kilograms before the division. The result appears instantly along with your category: underweight below 18.5, normal from 18.5 to 24.9, overweight from 25 to 29.9, and obese at 30 and above, following the World Health Organization thresholds.

Everything happens in your browser using plain JavaScript. Nothing you type is ever uploaded, stored, or sent to a server, so your height and weight stay on your own device. That also means the calculation is instant and works offline once the page has loaded.

Concrete uses: checking where you sit before a doctor's visit, tracking a number over a weight-loss or fitness phase, filling in a form for gym membership or life insurance, or settling a friendly debate about units. Anyone can benefit, but it is especially handy for people juggling metric and imperial figures, since the toggle removes manual conversion errors.

A practical tip: measure your height without shoes and weigh yourself at a consistent time of day, ideally in the morning, for comparable results over time. Remember BMI is a screening figure, not a diagnosis. It does not distinguish muscle from fat, so athletes with high muscle mass often read as overweight despite being lean, and it is less reliable for the elderly, pregnant women, and growing children, who need percentile-based charts instead. Treat the number as one input among many, and use it to start a conversation rather than to draw a firm conclusion about your health.