Ponderal Index Calculator (Neonatal & Adult) | Corpulence Index

What is the Ponderal Index?

The Ponderal Index (also known as the Corpulence Index or Rohrer's Index) is similar to BMI but uses the Cube of height ($Weight/Height^3$) instead of the Square ($Weight/Height^2$).

This mathematical difference makes it valid for bodies that are shorter (babies) or much taller than average, treating the body more like a 3D volume rather than a 2D surface area.

Why Pediatricians Use It (IUGR)

Symmetric IUGR

Baby is small all over (Head, belly, and length are all small). PI is Normal. This usually indicates early pregnancy issues (chromosomal or infection).

Asymmetric IUGR

Baby has a normal length/head but a skinny belly (starving). PI is Low (< 2.2). This is the critical warning sign for placental insufficiency in the third trimester.

Frequently Asked Questions

Is Ponderal Index better than BMI?

For adults of average height, they are roughly equivalent. However, Ponderal Index is superior for very tall individuals (who are often falsely labeled overweight by BMI) and newborns. Because infants grow in volume rather than just height, the cubic formula (m³) captures their density better than the squared formula (m²) of BMI.

What is a normal PI for a newborn?

A healthy full-term baby typically has a Ponderal Index between 2.2 and 3.0 (g/cm³ × 100). A score below 2.2 suggests malnutrition or "wasting," meaning the baby did not get enough nutrients in the womb during the final trimester (Asymmetric IUGR).

Does a high PI mean gestational diabetes?

Often, yes. A Ponderal Index > 3.0 indicates Macrosomia (a baby that is heavy for its length). This is common when the mother has Gestational Diabetes, causing the fetus to store excess glucose as fat. These babies are at higher risk for hypoglycemia (low blood sugar) immediately after birth.

Can adults use this calculator?

Yes. In fact, some researchers argue it is fairer. Since the Ponderal Index treats the body as a 3-dimensional object (volume), it doesn't penalize tall people as harshly as BMI does. If you are over 6'2" and BMI says you are "Overweight," check your Ponderal Index—it might classify you as "Normal."

How do I measure my baby's length accurately?

Measuring an infant is tricky because they naturally curl up (fetal position). To get an accurate length for this calculation, lay the baby flat on a firm surface. Gently stretch the leg out completely straight until the foot is flexed (90 degrees) and measure from the top of the head to the heel.

References

Pediatrics (AAP Journal). Assessment of Fetal Growth.
World Health Organization (WHO). Child Growth Standards and Indicators.
Stanford Medicine. Neonatal Growth Charts.
National Institutes of Health (NIH). Ponderal Index in Neonates.

Tools & Data Verified by the EverydayCalculators Medical Research Team.

Last updated: January 2026.

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