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What Is the Ponderal Index?

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  • Written By: Douglas Bonderud
  • Edited By: Michelle Arevalo
  • Last Modified Date: 20 September 2014
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The ponderal index is a method of measuring obesity. This index is also known as PI, and was created by F. Rohrer in 1921. At that time it was referred to as the corpulence index. The term 'ponderal' refers to a value estimated, or arrived at, by weight.

Used to determine a person's leanness, the ponderal index shares characteristics with a more common tool, the body mass index (BMI). Both indices use a ratio of height and mass. Originally, the value of the PI was arrived at by dividing a person's mass, in kilograms, by their height in meters. The height value is cubed before being divided by the weight. An imperial units version of the ponderal index also exists, and uses a person's height in inches divided by the cube root of his mass in pounds.

A BMI value, in contrast, uses the person's weight divided by their height2. The normal BMI measurement for an adult who is 5 ft 11 in (180 cm) tall is between 12.49 and 13.92 on the ponderal index, if the value is computed using pounds and inches. The larger the value, the more obese the individual.

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This index is often used to assess newborns, and very low or high values are generally indicators of intrauterine growth issues. A study conducted in 1990 demonstrated a correlation between the ponderal index value of a newborn, and that of a later born sibling. Therefore, knowing the PI of the first child in a family can assist in determining prevailing uterine conditions, which can be helpful if a second child is conceived.

There are also other variants of this index. One uses a weight value in grams divided by height in centimeters3, and then multiplied by 100. This produces a normal value of 2.4 for a 12 month-old child. Another variation uses the cube root of a person's weight in kilograms, divided by their height in centimeters, and then multiplied by 1,000 — which results in an average of 21.75 to 24.00 for an adult who is 5 ft 11 inch (180 cm) tall.

An advantage of the ponderal system is that the resulting values are consistent across varying heights. Also, when the values are listed in kilograms per meter3, the ponderal index has the same units as a measure of density. Both the ponderal index and BMI require only one simple calculation, but the BMI is used far more often in popular culture. The ponderal index is now used most often for pediatric purposes.

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anon279412
Post 3

The Ponderal index is more accurate for tall people (I think short too). There are simple calculators for it online as well.

sweetPeas
Post 2

The body mass indicator that most people in this country use to find out where they stand in body mass is the BMI system. It's easy to calculate. In fact, there are BMI charts on the internet. You just have to find your weight and height on the chart and go to the bottom to find your body fat number.

When I figured mine out recently, I was a little shocked. I was creeping too far into the overweight section. There are four sections: underweight, normal, overweight and obesity.

Of course, this method or the ponderal index is not completely accurate, but it's a good indicator of risk for certain diseases. People who have a lot of muscle mass, senior citizens who have lost muscle, or people who are under five feet tall, don't fit accurately in the index.

Clairdelune
Post 1

The formula for determining the degree of obesity, the ponderal index, is a bit confusing for those of us who don't know the metric system well. I don't get the part about all the extra mathematics in this method. The BMI is much simpler.

I can understand why they use a different system (the ponderal index) for measuring newborns. The reason being that babies have much shorter legs than adults do. So, you couldn't very well use the same scale on adults as on babies and small children.

Thankfully, the BMI measurement for obesity in adults is very easy to calculate. The score you get can be a real wake-up call to change your lifestyle.

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