# Body Mass Index

## Body Mass Index

The Body Mass Index (BMI) of a person can be calculated based on his/her height and weight. The original formula for calculating BMI is:

Metric (kilogram and meter):

BMI = Mass ÷ Height^{2}

US Units (lb and inches):

BMI = 703 × Mass ÷ Height^{2}

The BMI is often used to categorize a person as underweight, normal weight, overweight, or obese.

- Underweight corresponds to a BMI of less than 18.5 (blue)
- Normal Weight corresponds to a BMI between 18.5 and 24.9 (green)
- Overweight corresponds to a BMI between 25 and 29.9 (yellow)
- Obese corresponds to a BMI between 30 and 39.9 (orange)
- Extremely Obese corresponds to a BMI of 40 or higher (red)

## BMI and New BMI

The above mentioned formula used for calculating BMI has been used for many years. However this formula is not very suitable for very tall and very short persons. An alternative new BMI formula is:

Metric (kilogram and meter):

New BMI = 1.3 × Mass ÷ Height^{2.5}

US Units (lb and inches):

New BMI = 917 × Mass ÷ Height^{2.5}

This new BMI formula will allow tall people to be a bit heavier before putting them in the category overweight. Short people can be a bit lighter before being classified as underweight.

The tool on this page has the option to calculate with the original BMI or with the New BMI formula.