How BMI Is Calculated
BMI is calculated by dividing your weight in kilograms by your height in meters squared. The formula is: BMI = weight(kg) / height(m). Despite its simplicity, this calculation has been used for over a century as a population-level health screening tool.
The History of BMI
The BMI scale was developed in the 1830s by Belgian mathematician Adolphe Quetelet, who was not a physician but a statistician. He was studying normal weight distribution across populations, not trying to define healthy versus unhealthy. It was not until the 1970s that physiologist Ancel Keys popularized BMI as a tool for individual health assessment.
What BMI Correlates With
Population studies show that BMI correlates with several health outcomes. People with BMI over 30 have higher rates of heart disease, type 2 diabetes, hypertension, and certain cancers. However, correlation is not causation, and BMI is just one of many risk indicators.
When BMI Is Misleading
- Athletes: High muscle mass increases weight without increasing health risk.
- Older adults: Muscle loss with age can mask excess body fat.
- Different ethnicities: Asian populations have higher health risks at lower BMI thresholds.
- Body composition: Two people with the same BMI can have very different body fat percentages.
Better Metrics to Use Alongside BMI
For a more complete assessment, use our BMI calculator alongside: waist circumference (should be under 40 inches for men, 35 for women), waist-to-height ratio (under 0.5 is ideal), and body fat percentage. No single number tells the whole story about your health.
Using Our BMI Calculator
Our calculator provides your BMI value and category, but also shows your healthy weight range. Use it as a starting point for conversations with your healthcare provider, not as a definitive diagnosis of your health status.