Ponderal Index
A leanness index that scales better for extreme heights.
Formula
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Example
70 kg, 1.75 m ⇒ 70 / 5.36 = 13.1
How it works
The Ponderal Index compares a person's mass with their height cubed, so it measures how body mass changes as overall size changes in three dimensions. Using h^3 instead of h^2 makes it less biased by very tall or very short body types than BMI, because mass tends to grow roughly with volume rather than just with surface area. It is mainly a size-adjusted leanness indicator, not a direct measure of health or body fat.
When to use it
Use this when you want a rough body-size adjustment that is especially helpful for people at unusual heights, such as in sports science, anthropology, or clinical screening. It is most useful for comparing lean build across individuals rather than diagnosing obesity or illness on its own.
Worked example, step by step
Step 1: Write the formula: PI = m / h^3 Step 2: Substitute the values: PI = 82 / (1.82)^3 Step 3: Calculate the height cubed: (1.82)^3 = 6.03 Step 4: Divide mass by height cubed: PI = 82 / 6.03 Step 5: Final answer: PI ≈ 13.6
Common mistakes to avoid
- Using height squared instead of height cubed
- Putting height in centimetres without converting to metres first
- Treating the result as a direct diagnosis of fitness or body fat
Did You Know?
Unlike BMI, the ponderal index stays fair for unusually tall or short people, so it is used for newborns.
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