Fat and slim are relative notions. While almost everybody can recognize a slim person when they see one, a fat person is much harder to identity, because we have different standards and preferences in what overweight really is.

One standardized measure of how fat people are is the Body Mass Index. Briefly known as BMI, this index is a measure of a person's weight in relation with the height of that person. Because it is cheap and simple, it can be used on a large scale worldwide for screening people who might have weight issues. Under no circumstances a diagnosis should be set based solely on the BMI. It is not its purpose and it doesn't reflect any data regarding the health status of that person, nor can it give indications on the percentage of body fat. So, after the initial sceening is done, more precise and thorough tests and medical investigations are required before a diagnosis can be set and a treatment prescribed.

Nevertheless, for simple people who just want to keep their body weight under control, the Body Mass Index is an excellent alarm signal to stop you from eating all those ice creams and drinking all those beers.

If you want to see how fat you are according to this index, you can input your data in this BMI calculator and see it for yourself if you are OK, you need to eat more, or you need to learn some tips to lose weight.