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 meters. You take your weight in kilograms, divide it by your height in meters, and then divide again by your height. For example, a person weighing 70 kg and 1.75 m tall has a BMI of 70 divided by 1.75 and then by 1.75 again, which is 22.9 kg/m². The calculator above does this automatically and shows the category you fall into.

According to the World Health Organization, in adults BMI values are interpreted as follows [1]:

• below 18.5 — underweight range;
• 18.5 to under 25 — normal weight range;
• 25 to under 30 — overweight range;
• 30 to under 35 — obesity class I range;
• 35 to under 40 — obesity class II range;
• 40 or above — obesity class III range.

BMI does have its limitations, though. It cannot tell the difference between muscle and fat. It also ignores fat distribution, and abdominal fat is the riskier kind. 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. About where the fat sits, the waist-to-height ratio says more, and it asks for a single extra measurement.

Excess weight, especially fat around the abdomen, increases insulin resistance (your body responds less well to its own insulin, and the pancreas has to produce more) and is one of the most important risk factors for type 2 diabetes. A high BMI does not mean you will necessarily develop diabetes. Losing weight, even a modest amount, significantly lowers this risk. In people who already have diabetes, weight loss also improves blood glucose control.