BMI Calculator.

Body Mass Index is weight in kilograms divided by height in meters squared. It was designed in the 1830s by Adolphe Quetelet as a population-level descriptor — not a body composition tool. At the individual level, it has a real limitation: it cannot distinguish muscle from fat. A 6-foot, 220 lb rugby player and a 6-foot, 220 lb desk worker share a BMI of 29.8. They do not share metabolic risk.

BMI does correlate, at the population level, with all-cause mortality in a J-shaped curve: lowest risk roughly at BMI 22–25, rising sharply above 30 and below 18.

Waist-to-height ratio (WHtR) is a simpler measurement that correlates more tightly with visceral adiposity — the metabolically active fat around the organs. A useful heuristic: keep your waist below half your height. WHtR under 0.5 is associated with the lowest metabolic risk regardless of total body weight.

WHtR outperforms BMI for predicting type 2 diabetes, cardiovascular disease, and metabolic syndrome in meta-analyses across age and ethnicity groups. If your BMI says one thing and your WHtR says another, weigh the WHtR more heavily.

If both numbers are in the healthy range, do not optimize further — additional weight loss past this point shows diminishing returns and elevates muscle-loss risk. If WHtR is elevated, the lever is visceral fat: that responds to a calorie deficit, resistance training, and reduced refined-carb intake. If BMI is elevated but WHtR is not, you may be a muscular outlier where BMI overstates risk.