BMI Calculator

What BMI is

Body Mass Index (BMI) is a simple screening figure calculated from height and weight — specifically, weight in kilograms divided by height in meters squared (or the imperial equivalent: weight in pounds × 703, divided by height in inches squared). It was originally developed in the 1830s as a population-level statistical measure, not a diagnostic tool for individuals, and that origin is part of why it's best understood as a rough starting point rather than a complete picture of anyone's health.

This calculator supports both metric and imperial units and returns your BMI value along with the standard category it falls into — underweight, normal weight, overweight, or obese — based on the ranges used by major health organizations.

What BMI does and doesn't capture

BMI uses only height and weight, so it can't distinguish between muscle, fat, and bone density — a very muscular person can register as "overweight" on the BMI scale despite having low body fat, and BMI categories were developed primarily using data from adult populations, so they apply less precisely to athletes, older adults, pregnant people, and children, who are typically assessed with different tools entirely. It also doesn't account for where body fat is distributed, which some research suggests matters for health outcomes independent of overall BMI.

For these reasons, BMI is best treated as one general screening data point among many, not a definitive verdict on anyone's health status.

Common use cases

People use a BMI calculator as a quick, private way to check where their height and weight fall relative to standard reference ranges, often ahead of a doctor's visit or as part of general health tracking. Healthcare providers use BMI as one initial screening measure among several when assessing a patient. Researchers and public health organizations use BMI at a population level, where its statistical limitations matter much less than they do for interpreting any single individual's result.

Using your result thoughtfully

If your BMI result surprises you or you have questions about what it means for your health, a healthcare provider can offer a fuller assessment that accounts for your specific body composition, medical history, and other factors this calculator simply doesn't have access to. This tool is meant as a quick, private, informational starting point — not a diagnosis or a recommendation to make any specific change to your diet or exercise.

Where BMI is still useful

Despite its limitations for any one individual, BMI remains widely used because it's simple, requires no special equipment beyond a scale and a height measurement, and correlates reasonably well with health risk across large populations, which is why it continues to show up in public health research and general screening guidelines. Its value comes from being an easy, free, repeatable starting measurement — something you can track over time for yourself, or a quick first data point a clinician can use before deciding whether a more detailed assessment (like body fat percentage, waist circumference, or metabolic testing) is worth pursuing.