What this calculator does
BMI divides weight by height squared, which is dimensionally odd: weight scales with volume, and volume scales with the cube of length. The ponderal index uses height cubed instead, which is geometrically the more consistent choice.
In practice BMI is entrenched and the ponderal index is not, with one exception. It is used routinely in neonatal care, where it flags babies who are unusually thin or stocky for their length.
The formula
Divide weight in kilograms by height in metres cubed. Adult values typically land between about 11 and 15 kg/m³.
| Term | Meaning |
|---|---|
| Ponderal index | Weight divided by height cubed, in kg/m³. |
| Corpulence index | Another name for the same measure. |
| Neonatal use | In newborn assessment it is expressed in g/cm³ and used to identify growth restriction. |
The inputs explained
| Field | What to enter |
|---|---|
| Weight (kg) | Weight in kilograms. |
| Height (cm) | Height in centimetres. |
When to use it
Comparing across very different heights
BMI systematically flatters tall people and penalises short ones; cubing height reduces that.
Neonatal growth assessment
The index identifies newborns whose weight is out of proportion to their length.
Understanding the criticism of BMI
The dimensional argument is easiest to see by comparing the two directly.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How does weight move the index?
The same height at three body weights.
| Weight | Ponderal index | Typical adult range |
|---|---|---|
| 60 kg | 11.20 kg/m³ | about 11 - 15 kg/m³ |
| 75 kg | 13.99 kg/m³ | about 11 - 15 kg/m³ |
| 95 kg | 17.73 kg/m³ | about 11 - 15 kg/m³ |
Questions
If it is more consistent, why is BMI used instead?
Largely history and inertia. BMI has decades of population data and clinical thresholds behind it, which the ponderal index does not. Being dimensionally tidier has not been enough to displace that.
Does cubing height actually fix the problem?
Partly. People do not scale as perfect geometric solids, so neither squaring nor cubing is exactly right. Empirically the best exponent falls somewhere between 2 and 3 and varies by population.
Why is it used for newborns?
Because it distinguishes symmetrical from asymmetrical growth restriction. A baby who is light for their length has a different clinical picture from one who is small overall, and the index separates the two.
What is a normal adult value?
Roughly 11 to 15 kg/m³, though the index lacks the extensively validated thresholds BMI has. It is better used for comparison over time than read against a fixed band.
For the standard weight-for-height measure, see the BMI calculator. For a shape measure using waist, see the body roundness index calculator.