If you are looking for a more accurate measure than Body Mass Index, check out this ponderal index calculator. The ponderal index, also known as a corpulence index or Rohrer’s index, can help you in determining if you are overweight, underweight, or just right, as the BMI value does. However, PI has higher sensitivity and specificity, so if you are a tall person, your BMI may show that you are obese, but it’s not necessarily true. Infant ponderal index is used in pediatrics: to assess whether a newborn baby is malnourished, healthy or overweight, as well as in conditions such as intrauterine growth restriction where fetus grows poorly in mother’s womb. Read on to know more about ponderal index formulas and ponderal index normal ranges.
The Ponderal Index
It is the ratio of the person’s height to weight. It can be calculated for both adult, kids and infants. This method is normally used by pediatrics. It can also be used to identify infants whose soft tissue mass is below the normal stage of skeletal development.
Ponderal index formula
Ponderal means estimated or ascertained by weight. Ponderal index is an improved version of body mass index – BMI uses height to the second power:
BMI = weight / height²
whereas ponderal index use height³ – which makes more sense as our bodies are 3-dimensional structures, not 2D!
PI = weight / height³
BMI works well for people of average height (~5 ft 6 in / 170 cm), but if you are a very tall person, your BMI value will most probably indicate the overweight. If you are short, BMI is a favorable measure showing normal weight even if you need to lose a few pounds.
For adults the basic weight unit in PI calculation is kg and height expressed in meters. For infants and newborn babies, weight is usually shown in grams and height in centimeters:
- PI_adult = weight [kg]/ height [m]³
- PI_child = weight [g]/ height [cm]³ = 0.1 * PI_adult
Challenges with Ponderal Index
Like all “simple” health calculators (such as BMI), Ponderal Index is an indicator of health (among a number of other factors) not an absolute measurement.
Some challenges with Ponderal Index include:
- It does not show a difference between people with lots of muscle and lots of fat – a very muscly person may have the same BMI as a person with a lot of fat.
- It does not show a difference between body types that may hold weight in different parts of their bodies
It is important to remember that Ponderal Index is an indicator and not an absolute measurement of health.