BMI Calculator
Enter your height and weight below, and this body mass index calculator outputs your BMI score and weight category instantly.
About
About BMI Calculator
BMI compares your weight against your height using a formula that's actually almost 200 years old, developed by a Belgian statistician named Adolphe Quetelet in the 1830s, long before it became a standard screening tool in medicine. A body mass index calculator applies that formula instantly, giving you a quick numeric score and the health category it falls into.
The metric formula divides weight in kilograms by height in meters squared. The imperial version looks different but produces the same result: multiply weight in pounds by 703, then divide by height in inches squared. Both versions exist purely to avoid forcing a unit conversion before you can even calculate your score.
It's genuinely useful to know what BMI doesn't measure, since that's where it gets misapplied. The formula has no way to distinguish muscle mass from fat mass or account for frame size, which is exactly why a muscular athlete with low body fat can register as "overweight" on a BMI scale despite being in excellent physical condition. It's a population-level screening tool, not an individual diagnosis.
Enter your height and weight in either metric or imperial units, and your BMI calculates immediately alongside the official category range it falls into, underweight, normal, overweight, or obese.
These category thresholds come from established public health guidelines rather than anything this tool invents on its own, 18.5 to 24.9 is considered the normal range, for reference. Everything calculates locally in your browser, so personal health data like height, weight, and the resulting score never gets uploaded anywhere.
FAQ
Frequently asked questions
What does BMI actually stand for?
Body Mass Index, a formula using weight and height to produce a general screening number for assessing whether someone falls into a typical healthy weight range for their height.
How exactly is BMI calculated?
Divide weight in kilograms by height in meters squared. In imperial units, multiply weight in pounds by 703, then divide by height in inches squared, both formulas land on the same resulting score.
Is BMI actually a reliable measure of someone's health?
It's a useful large-scale screening tool, but it has real limitations individually, since it can't distinguish muscle from fat or account for frame size. A heavily muscled athlete can register as overweight on a BMI scale despite carrying very little body fat.
What are the standard BMI weight categories?
Below 18.5 is classified as underweight, 18.5 to 24.9 as normal weight, 25.0 to 29.9 as overweight, and 30.0 or above falls into the obese category, per standard public health guidelines.
Does BMI get calculated differently for men versus women?
The mathematical formula itself is identical for adult men and women. Some clinical interpretation guidelines do account for typical physiological differences in body composition between the sexes, but the calculation itself doesn't change.
Is my height and weight data saved anywhere?
No, every calculation happens locally through client-side JavaScript. Your measurements are never stored or transmitted to a server.
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