The birth of the body mass index
The body mass index (or BMI) was devised between 1830 and 1850 by the sociologist, Lambert Adolphe Jacques Quetelet (and this is why the BMI is also sometimes referred to as the Quetelet Index).
The calculation is very simple, you divide the weight (in kg) by the height squared (in m). Therefore:
BMI = weight/ (height x height)
For example, an individual who is 1.75 cm tall and weighs 72 kg, will have a BMI of:
72/ (1.75x1.75) = 23.5
Please note that body mass index only takes into account height and weight, and doesn't consider other contributing factors such as age, sex, genetic factors, nutrition, living conditions, health, etc.
One limitation of this calculation is linked to people with significant muscle mass, such as bodybuilders and athletes who have pronounced muscles. In these cases, the result tends to overestimate the body fat percentage.
New BMI formula
In 2013, researchers at Oxford University developed a new BMI formula:
BMI (Oxford 2013) = 1.3 x weight/ height2.5
For example, the same individual who is 1.75 cm tall and weighs 72 kg, will now have a BMI of:
1.3 x 72/ 1.752.5 = 23.1
You will immediately notice that the BMI is slightly lower.
BMI and weight classification
The World Health Organization (WHO) has lent their support to these tables by classifying individuals with terms such as "underweight" or "overweight/ obese" depending on their BMI score.
| Weight classification | Min | Max |
|---|---|---|
| Class III obesity (morbid) | = 40 | |
| Class II obesity (severe) | 35 | 39.9 |
| Class I obesity (moderate) | 30.0 | 34.9 |
| Overweight | 25.0 | 29.9 |
| Normal (ideal weight) | 18.5 | 24.9 |
| Slightly underweight | 17. 5 | 18.49 |
| Visibly underweight (moderate thinness) | 15.5 | 17.49 |
| Severely thin (severe thinness) | <15.5 |
Calculating body fat percentages
BMI is not the only parameter that we can analyse.
Thanks to Wilmore and Behnke's formula, we can also estimate body fat percentage.
In order to work out lean body mass, this formula takes weight (kg) and waist circumference (cm) into account, so:
LBM = 44.636 + 1.0817 x weight - 0.7396 x waist circumference
If a man weighs 75 kg and has a 83 cm waist circumference, then his lean body mass value will be:
44.636 + 1.0817 * 75 - 0.7386 x 83 = 64.4kg
The body fat will then be 10.6kg (75 to 64.4).
So the body fat percentage, will therefore be 14.1% (10.6/ 75).
Important note
Wilmore and Behnke's formula for calculating lean body mass and body fat is more reliable for men.
The results are not reliable for women.
BMI calculator, Morphology, BF%, Lean Body Mass, Body Fat
With just a few of your details, this calculator works out your BMI (and weight classification), morphology, estimated body fat percentage and give you an indication of your lean body mass and body fat.
