The Body Mass Index

The Body Mass Index (BMI) is a rough way to determine if your body is in a healthy state. It is not perfect, but it does provide a simple way to see if you have anything to worry about.

Use my tool to check your BMI here

The Body Mass Index works by taking your weight, and dividing it by your height (squared). The reason that the Body Mass Index uses your height and weight in this way is because you would expect two people who are of different heights to have different weights - even if they are equal.

A relatively overweight 5ft person would look quite skinny if they were stretched to be 6ft tall.

When the Body Mass Index doesn't work

The Body Mass Index doesn't always work. It is common for men involved in sports to look quite fit, yet be obese when they put their numbers into a BMI Calculator. This is because muscle weights a lot more than fat, but takes up less room. Therefore, even if have virtually no fat, your muscle makes you very heavy.

The BMI also ignores bone structure, eating habits, etc.

What is a good Body Mass Index?

Run your figures through a BMI calculator (click here). If your BMI is under 18.5, you are classed as underweight. Between 18.5 and 25, you are in the perfect range. Above 25, and you are overweight.

If you are under or overweight (for example 15 or 30 on the BMI scale) you should consult medical advice - as your health may be at risk. This is even more important if your weight drops or increases in a short space of time.

For the reasons outlined above, the Body Mass Index is simply as indicator - not a perfect tool. If you are sleeping well, are getting regular exercise and have enough energy to get you through your day, your body will have found an equilibrium.