Understanding body mass index_weight

Body Mass Index or BMI is a way of checking to see if you are a healthy weight. BMI uses your height and weight to calculate if you are a healthy weight, overweight or underweight. You can check your BMI using a BMI chart or there are many websites that have a BMI calculator.


Understanding BMI

When you calculate your BMI, you will get a number at the end.

If your number is less than 18.5 then you are probably underweight.

If your number is between 18.5 and 25, then you probably have a healthy weight.

If your number is between 25 and 30 then you are probably overweight.

If your number is over 30 then you are probably obese.


BMI Category
Less than 18.5 Underweight
18.5-25 Healthy Weight
25-30 Overweight
30 or more Obese

People come in all shapes and sizes. This is why there is a wide range of weights-for-heights in each category.This helps to take into account a smaller or larger frame for people who are the same height.

What does being a healthy weight mean?

Sometimes people are confused about BMI. It is important to remember that BMI has nothing to do with what you look like! A slim person with a lot of muscle can have a higher BMI than and larger person with a lower BMI whose weight mainly comes from fat.

BMI is a health index

Someone whose BMI is between 18.5 and 25 has a healthy weight. People with BMIs between 18.5 and 25 have less chance of developing diseases like cancer, heart disease and diabetes. As BMI goes up, the chances of developing these diseases also increases. The risk for these diseases particularly goes up once BMI is over 30.This is one of the reasons that it is useful to try to reduce your BMI if you are in the overweight or obese category.

BMI, Fat and Muscle

One problem with BMI is that it cannot tell the difference between weight coming from fat and weight coming from muscle. This means that people with a lot of muscle (e.g. International rugby players, body builders) will often have a BMI higher than 25 but will still be healthy.This is why you must always check your waist measurement at the same time as your BMI.

Checking your Waist

The best way to get an idea about whether or not you are a healthy weight is to check your waistline. You need to measure halfway between the top of your hips and your lowest rib (across your belly button is a good place).

Try to be:

Men – Less than 90cm or 37 inches

Women - Less than 80cm or 32 inches