How to Calculate Ponderal Index

What is Ponderal Index?

The Ponderal Index (PI) divides weight by height cubed, making it more scale-independent than BMI for very tall or short individuals. Widely used in neonatal medicine for growth assessment.

Formula

PI = Weight (g) / (Length (cm)^3) × 100; or PI = Weight (kg) / (Height (m)^3); Normal: 2.2–3.6; < 2.2 = thin; > 3.6 = stocky

Weight: Body weight (kg (or grams for infants))
Length: Length / height (cm (or meters))
PI: Ponderal index (Unitless (or g/cm³))

Step-by-Step Guide

1PI = Weight (kg) / Height (m)³
2Normal adult range: 11–14 kg/m³
3Used in neonates to assess intrauterine growth restriction
4More appropriate than BMI at extremes of height

Worked Examples

Input

Weight 68 kg, height 1.72 m

Result

PI = 68 / 5.088 = 13.4 kg/m³ (Normal)

Frequently Asked Questions

How does PI differ from BMI?

BMI uses height squared; PI uses height cubed. PI more sensitive to changes in weight relative to height. PI better for very short people (children, dwarfism); BMI for adults.

Why is PI useful for newborns?

Intrauterine growth restriction (IUGR) detection. Low PI = thin baby (poor nutrition in womb). Normal PI but low weight = prematurity. Helps distinguish causes of low birth weight.

What's a normal newborn PI?

Newborns: 2.2–3.0 typical. Low (< 2.0) suggests IUGR. High (> 3.5) suggests well-nourished larger baby. Track over first year; gradually lowers as child grows taller.

Ready to calculate? Try the free Ponderal Index Calculator

Try it yourself →