BMI calculator (body mass index)

Body mass index (BMI) is a particular ratio between weight and height, used to estimate whether a person is underweight, at a suitable weight, or overweight for their height. It is expressed in kg/m². BMI does not measure body fat directly, but it correlates with it fairly well, which is why it is used as a quick screening tool.

BMI is obtained by dividing your weight in kilograms by the square of your height in metres. You take your weight in kilograms, divide it by your height in metres, and then divide again by your height. For example, a person who weighs 70 kg and is 1.75 m tall has a BMI of 70 divided by 1.75 and then divided by 1.75 again, which is 22.9 kg/m². The calculator above does this automatically and also shows the category you fall into, according to the World Health Organization classification.

According to the World Health Organization, in adults a value below 18.5 means underweight, between 18.5 and 24.9 normal weight, between 25 and 29.9 overweight, between 30 and 34.9 obesity class I, between 35 and 39.9 obesity class II, and 40 or above obesity class III. BMI does have its limitations, though. It cannot tell the difference between muscle and fat, it does not take fat distribution into account (abdominal fat is riskier), and it is not interpreted the same way in children, athletes, pregnant women, or older adults. That is why it is a starting point, not a conclusion.

Excess weight, especially fat around the abdomen, increases insulin resistance and is one of the most important risk factors for type 2 diabetes. A high BMI does not mean you will necessarily develop diabetes, but losing weight, even a modest amount, significantly lowers this risk and improves blood glucose control in people who already have diabetes.