Body composition calculator
Ponderal index calculator
Weight divided by height cubed — the index that does not punish you for being tall. See it next to your BMI. Free, instant, no sign-up.
An index is a description, not a target. The coach starts from what you want to change.
What is the ponderal index?
The ponderal index — also published as Rohrer's index, and sometimes the corpulence index — is your weight divided by the cube of your height, in kg/m³. It answers the same question BMI does, with one difference in the arithmetic that turns out to matter: it divides by height cubed rather than height squared.
Why cubed rather than squared
Scale a body up uniformly and its mass grows with the cube of its height, because mass fills a volume and volume is three-dimensional. BMI divides by height squared, which is dimensionally wrong for a solid object. The consequence is systematic: at identical body composition, BMI drifts upward with stature, so tall people read heavier than they are and short people read lighter. Cubing removes that drift. This is why paediatricians and neonatologists, who deal with bodies changing size fast, reach for the ponderal index far more often than for BMI.
So why is BMI still the standard?
Because the argument above is mathematical and the choice was empirical. Across the middle of the adult height distribution, BMI's error happens to correlate better with actual body fat than the ponderal index's does, and BMI has a century of population data and cutoff tables behind it that the ponderal index does not. Neither index measures fat; both are weight-for-height ratios that stand in for it. The ponderal index earns its place exactly where BMI is weakest — at the tails, for the very tall and the very short, where BMI's drift with stature is largest.
What it cannot tell you
The same thing BMI cannot: muscle from fat. A dense, well-trained body and an untrained one of the same mass and height score identically. There is also no accepted clinical cutoff table for ponderal index in adults the way there is for BMI, which is why this page shows the roughly 11 to 15 kg/m³ band that covers most adults and stops there rather than handing you a category. If you want a number that tracks body fat, measure body fat.