Ponderal Index Formula
Just like BMI, the Ponderal Index uses your weight and height only. The difference is that it cubes your height instead of squaring it. This minor difference makes it more precise than BMI for very short or very tall people.
The Ponderal Index Formula
In metric units:
PI = Weight (kg) / Height³ (m)
For imperial units (pounds and inches), you need a conversion factor:
PI = (Weight (lbs) × 703) / Height³ (in)
Example Calculation
Let's calculate the Ponderal Index for someone with these measurements:
- Height: 175 cm (1.75 m)
- Weight: 70 kg
Calculation:
PI = 70 / (1.75)³ = 70 / 5.359 = 13.1
A result of 13.1 falls in the "Normal" range - meaning healthy body proportions.
Ponderal Index Categories
| Category | Ponderal Index |
|---|---|
| Underweight | < 11 |
| Ideal | 11-13 |
| Normal | 13-15 |
| Overweight | 15-17 |
| Obese | > 17 |
Why Cube the Height?
BMI squares your height. The Ponderal Index cubes it:
BMI = Weight / Height²PI = Weight / Height³
Bodies are 3-dimensional, hence we cube of height. The result is a formula that offers more accurate results for very short or very tall people.
History
Swiss physician Fritz Rohrer created this formula in 1921 - before BMI became popular. BMI eventually won out, but many researchers consider the Ponderal Index to be superior.