Calculate your Body Mass Index (BMI) instantly from your height and weight.
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Body Mass Index (BMI) is a simple screening measure calculated by dividing your weight in kilograms by the square of your height in meters. It is widely used by health organizations worldwide as a quick indicator of whether a person's weight falls within a healthy range for their height. While BMI does not directly measure body fat and can be less accurate for athletes or older adults, it remains a useful first step for tracking general health trends over time. A result between 18.5 and 24.9 is generally considered a healthy range for most adults. The formula was developed in the 1830s by Belgian statistician Adolphe Quetelet as a population-level statistical tool, not an individual diagnostic test — a distinction that explains most of the criticism it receives today. It remains the World Health Organization's standard screening tool for classifying weight categories across large populations, where it's genuinely useful for tracking trends, even though it can't distinguish muscle mass from fat mass in any one individual.
Body Mass Index was developed in the 1830s by the Belgian statistician Adolphe Quetelet, originally as a population-level statistical tool, not an individual diagnostic test — a distinction that explains most of the criticism the formula receives today. The math itself is simple: weight in kilograms divided by height in meters squared. Because it only needs two measurements, it became the World Health Organization's standard screening tool for classifying underweight, healthy weight, overweight, and obesity categories across entire populations, where it remains genuinely useful for tracking trends over time and across large groups.
The well-documented weakness is that BMI cannot distinguish muscle mass from fat mass, since it only looks at total weight relative to height. A bodybuilder and a sedentary person of the same height and weight can land in the same BMI category despite having very different amounts of body fat and very different health risk profiles. BMI also tends to be less reliable at the extremes of height, in older adults (who naturally lose muscle mass with age even at a stable weight), and across different ethnic groups, where the relationship between BMI and health risk shifts somewhat — several health organizations use lower BMI thresholds for increased risk in South and East Asian populations, for example.
Because of these limits, most clinicians treat BMI as a fast first-pass screening number rather than a stand-alone diagnosis — a high or low BMI is a prompt to look further (at waist circumference, body fat percentage, blood work, or a clinical exam), not a conclusion on its own. Pairing a BMI result with a waist-to-height ratio or body fat percentage calculator gives a noticeably fuller picture of body composition than either number alone, which is why this calculator links to both as related tools.
For most adults, a BMI between 18.5 and 24.9 is considered a healthy weight range.
BMI only uses weight and height, so it can't tell whether extra weight comes from muscle or fat — this is why very muscular people are sometimes misclassified as "overweight" despite low body fat.
BMI can overestimate body fat in very muscular people, since it doesn't distinguish muscle from fat.
The same BMI formula is used for both, though healthy body fat percentages differ by sex.