Body mass index, or BMI, is a rough measure of body weight that estimates whether your weight is healthy for an average person of your height. BMI is not a suitable measurement for children or very muscular athletes. For the rest of us, however, it's a useful tool that can help to identify and maintain the appropriate weight range for a given height.
Things You'll Need
 Calculator

Measure the height, in inches, of the person whose BMI you want to convert to pounds. One foot is 12 inches, so a 5foot6inch person would be (5 x 12) + 6 inches tall, or 66 inches.

Calculate weight from BMI using this formula:
(BMI / 703) x (height in inches x height in inches) = weight in pounds
As an example, if a person were 66 inches tall, and had a BMI of 27, his weight would be (27 / 703) x (66 x 66), which is 0.0384 x 4,356, or 167 pounds.

Check your results. Enter the height and weight into this formula to convert to BMI:
weight in pounds / (height in inches x height in inches) x 703 = BMI
The answer should be the BMI you started with. (Note that you may have to round the answer up or down to get a whole number.) If the BMI is different, there is an error in your calculations.
Tips & Warnings
 BMI values represent points within categories that describe how close an individual is to the ideal height/weight ratio for adults. The World Health Organization defines eight categories, from severe thinness to obese class III.
References
 Photo Credit Body image by Snezana Skundric from Fotolia.com