# BMI Prime Calculator

LAST UPDATE: April 8th, 2018

## What is BMI Prime?

BMI Prime is a ratio of a person’s BMI to the upper-level weight limit of “healthy weight”.
It is intended to give a quick answer to how far an individual differs upper weight limits, as well as an easy comparison between people whose upper BMI weight limits are different.
A BMI Prime between 0.74 – 1.00 is considered optimal for health.
Upper weight limits for “healthy weight” are typically 23 in Southeast Asia, and 25 in the rest of the world.

Category BMI Prime BMI Range
Very severely underweight Less than 0.60 less than 15.0
Severely underweight 0.60 – 0.64 15.0 – 16.0
Underweight 0.64 – 0.74 16.0 – 18.5
Healthy weight 0.74 – 1.0 18.5 – 25
Overweight 1.0 – 1.2 25.0 – 30.0
Moderately obese 1.2 – 1.4 30.0 – 35.0
Severely obese 1.4 – 1.6 35.0 – 40.0
Very severely obese Over 1.6 more than 40.0

## How to Calculate BMI Prime

In pounds and inches, BMI Prime is calculated as:
$\frac{\frac{\text{Mass(lbs)}}{\text{Height (inches)}^2}\times703}{\text{Upper Body Weight Limit}}$
In meters and kilograms, BMI Prime is calculated as:
$\frac{\frac{\text{Mass (kg)}}{\text{Height (m)}^2}}{\text{Upper Body Weight Limit}}$

## Example

Example 1:
A person has a mass of 165 lbs and is 5 foot 10 inches (70 inches) tall. The upper body weight limit for the region they are using is 25.
$\text{BMI}=\frac{\frac{165}{70^2}\times703}{25}$
$\text{BMI}=\frac{\frac{165}{4900}\times703}{25}$
$\text{BMI}=\frac{0.3367\times703}{25}$
$\text{BMI}=\frac{23.67}{25}$
$\text{BMI}=0.9468$
This person’s BMI Prime is 0.9468.
Example 2:
A person has a mass of 75kg and is 1m 78cm (1.78m) tall. The upper body weight limit for they region they are using is 25.
$\text{BMI}=\frac{\frac{75}{1.78^2}}{25}$
$\text{BMI}=\frac{\frac{75}{3.1684}}{25}$
$\text{BMI}=\frac{23.67}{25}$
$\text{BMI}=0.9468$
This person’s BMI Prime is 0.9468.

## Challenges with BMI Prime

BMI Prime is a simplified version of BMI. However, it still faces many of the same challenges as the BMI system.
BMI was initially intended to be an objective measurement of larger populations instead of individuals.
Because of its simplicity and ease to measure, it has become common in medical and health fields to monitor BMI along with other variables.
BMI is not an absolute “score” – it is merely an indicator.
Some challenges with BMI 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 BMI is an indicator and not an absolute measurement of health.