BMI Calculator

Body Mass Index, or BMI, is a simple screening number that estimates whether your weight is in a healthy range relative to your height. It doesn't measure body fat directly, and it can't tell the difference between muscle and fat, but because it only needs two easy measurements, it's widely used as a quick first check by doctors, insurers, and public health researchers.

The formula differs slightly depending on which units you use. In metric units, BMI is your weight in kilograms divided by the square of your height in meters. In imperial units, it's your weight in pounds divided by the square of your height in inches, multiplied by 703 to land on the same scale as the metric version. Either way, you end up with a single number that falls into one of four standard categories: under 18.5 is considered underweight, 18.5 to 24.9 is considered a normal weight, 25 to 29.9 is considered overweight, and 30 or above is considered obese.

Because BMI only looks at height and weight, it has well-known blind spots. A muscular athlete can register as "overweight" even with very little body fat, since muscle is denser than fat. Older adults can have a "normal" BMI while carrying more body fat and less muscle than the number suggests. BMI also doesn't account for where fat is distributed on the body, which matters for health risk, or for differences across sexes and ethnic groups.

For these reasons, BMI is best treated as a starting point for a conversation, not a diagnosis. It's a useful, free, instant way to see roughly where you stand, but it works best alongside other measurements, like waist circumference or body fat percentage, and a conversation with a healthcare provider who knows your full health picture.