How to Calculate BMI and Ideal Body Weight

BMI (Body Mass Index) is a number that indicates how fit and healthy you are. It is based on the ratio of your weight and your height squared. A high BMI corresponds to having excess body weight, while a low BMI corresponds to being underweight. According to the chart used by the National Institute of Health, a healthy BMI is between 18.5 and 24.9.

If you measure your weight and height in metric units, the formula for BMI is

kilograms/(meters²), or
(10000)kilograms/(centimeters²).

If you measure your weight and height in Imperial units, the BMI formula is

(703.01)pounds/(inches²).

The NIH has a BMI chart that explains the significance of each BMI level.


below 16.5 severely underweight
16.5 to 18.4 underweight
18.5 to 24.9 healthy
25 to 30 overweight
30.1 to 40 obese
above 40 morbidly obese

Computing Ideal Body Weight Based on BMI

You can determine your ideal body weight (IBW) according to your height and the ideal BMI range. To find the lower end of your ideal weight range, evaluate one of the following formulas:

(18.5)(inches²)/703.01 (for weight in lbs)
(18.5)(centimeters²)/10000 (for weight in kg)
(18.5)(meters²) (for weight in kg)

To compute the upper end of your ideal weight range, evaluate one of the following formulas:

(24.9)(inches²)/703.01 (for weight in lbs)
(24.9)(centimeters²)/10000 (for weight in kg)
(24.9)(meters²) (for weight in kg)

Example: Suppose a person is 68 inches tall. If you compute

(18.5)(68²)/703.01 = 121.68 lbs, and
(24.9)(68²)/703.01 = 163.78 lbs

then you can see that the person's ideal weight is between 122 and 164 pounds.

© Had2Know 2010