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.
Measure the height, in inches, of the person whose BMI you want to convert to pounds. One foot is 12 inches, so a 5-foot-6-inch 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.
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.