Body Mass Index Formula

In its simplest form, Body Mass Index is calculated as weight over height squared. This works as is for Metric Calculations, and has a multiplier added for Imperial Calculations.

Metric BMI Formula
BMI = Weight (Kg) / Height (Meters) x Height (Meters)

English BMI Formula
BMI = ( Weight (Lb)/ Height (in) x Height (in) x 703

BMI Accuracy

The Body Mass Index was originally designed as a broad representation of populace obesity levels purely for statistical purposes. As such is can be useful, but when applied to Medical uses then other factors such as fat/muscle ratio, fitness levels, bone structure, ethnic background and gender can all have an effect on the accuracy of the BMI formula ad so should be taken into consideration.

BMI is also affected by height with shorter people having and overall lower Body Mass Index, and age with older people seemingly having a normal BMI with hidden fat reserves replacing muscle tissue with an increased sedentary lifestyle.

All in all, the BMI is a useful guide, but all factors need to be taken into account when making a diagnosis.