# BMI to BMI Prime Converter

LAST UPDATE: September 24th, 2020

## Definition – What is the difference between BMI and 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 generally considered optimal for health.
Upper weight limits for “healthy weight” are typically 23 in Southeast Asia, and 25 in the rest of the world.

## Formula – How to Convert between BMI and BMI Prime

The equation to convert from BMI to BMI Prime is: BMI Prime = BMI / Upper Body Weight Limit
The equation to convert from BMI Prime to BMI is: BMI = BMI Prime x Upper Body Weight Limit
The Upper Body Weight limit is the upper limit of the “healthy weight” category on the selected BMI scale. For most regions it is 25, with many Southeast Asian scales, the upper limit is 23.

### Example

Example 1:
A person has a BMI of 28.22, and the upper weight limit for them is 25.
BMI Prime = 28.22 / 25
BMI Prime = 1.129
This person’s BMI Prime is 1.129.
Example 2:
A person has a BMI Prime of 0.882, and the upper weight limit for them is 25.
BMI = 0.882 x 25
BMI = 22.05
This person’s BMI is 22.05

### Challenges with BMI and BMI Prime

BMI (as well as BMI Prime) 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 and BMI Prime 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 and BMI Prime are indicators and not an absolute measurement of health.