FAQ: Body mass index

How is the body mass index (BMI) calculated?

The most common way to think about whether you are overweight is to look at your body mass index (BMI). This is calculated by comparing your weight with your height, using the following formula:

BMI = weight in kilograms / (height in metres)2

Example: I weigh 74kg and my height is 1.87m, so my BMI is
74 / (1.87)2 = 21.2 kg per m2

What is a normal body mass index?

Status Body Mass
Underweight < 18.5
Normal 18.5 - 25
Overweight 25 - 30
Obese 30 - 35
Very obese 35 - 40
Extremely obese > 40

Does the BMI scale apply to everyone?

No. The BMI scale, and other similar methods based on comparing weight and height, are fairly crude and should be treated with caution. You may weigh a lot for your height because you have excess fat (which might be a problem). But you may have a high BMI because you are have a stocky build, or because you work out in the gym and have more than average lean muscle tissue. This will increase your weight relative to your height, but it does not mean that you are too fat.

The BMI scale used here is only suitable for adults aged 20-65 it is not appropriate for all ethnic groups.

See also