Calculating BMI

Diet and Weight Loss Tutorial

BMI stands for Body Mass Index, which is an assessment of your weight relative to your height. The equation is:

weight in kg / (height in m x height in m)

The BMI Calculator will do the math for you. And don't worry if you measure yourself in pounds, feet or centimeters, or even stones, we'll convert the numbers to fit the equation.

The results of the BMI calculation are categorized as follows:

BMI Category
Below 18.5 Underweight
18.5 - 24.9 Normal Weight
25 - 29.9 Overweight
30 - 39.9 Obese
40 and above Morbidly Obese

You will be able to estimate a healthy weight for your height in our next topic, Calculating Ideal Weight.

Notes on Accuracy

The BMI equation is extremely popular, yet it can be extremely inaccurate and misleading.

The equation does not take into account body composition, a measure of the percentages of muscle and fat composing your body. It is therefore less accurate if you have a non-typical amount of muscle.

This is because while a person with an above average amount of muscle is likely to be healthier because of it, the equation simply interprets the added muscle as fat and overestimates obesity. The problem is compounded by the fact that muscle weighs more than fat.

Conversely, with older persons and others with a below average amount of muscle, the BMI equation underestimates obesity.

Because of this discrepancy, if you are gaining (or losing) a significant amount of muscle with your weight loss program, checking how your clothes fit might be a better way to monitor your progress than recalculating your BMI.

A more accurate assessment can be made by measuring your body fat percentage as discussed in the topic Calculating Body Composition.

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