⚖️BMI Calculator

Body Mass Index (BMI) is a simple screening number that compares your weight to your height. It's calculated as your weight in kilograms divided by the square of your height in metres (kg/m²).

Because it needs only height and weight, BMI is a quick, free way to flag whether your weight may be in a range that raises health risks. It's used worldwide by health bodies as a first-pass screen — not a full diagnosis.

The World Health Organization groups adult BMI into the categories in the table below: under 18.5 is underweight, 18.5–24.9 is a healthy weight, 25.0–29.9 is overweight, and 30 or above is in the obesity range (split into classes I–III).

These ranges apply to most adults aged 20 and over. A higher BMI is associated with greater risk of conditions such as type 2 diabetes and heart disease — but BMI alone doesn't tell the whole story (see below).

BMI doesn't distinguish muscle from fat or show where fat is stored, so it can be misleading for some people: very muscular athletes can read as 'overweight' while having low body fat, and older adults who have lost muscle may read as 'healthy' despite excess fat.

BMI is also not used the same way for everyone. For children and teens (2–19), age- and sex-specific percentiles are used instead. It isn't a guide during pregnancy. And risk can begin at a lower BMI in some populations — the WHO notes many Asian populations face higher risk at a BMI below 25. Treat your BMI as a starting point and discuss it with a healthcare professional.

To get a fuller picture, pair BMI with your waist measurement (a large waist signals more abdominal fat), and consider your diet, activity, blood pressure and family history. Two people with the same BMI can have very different health profiles.

Metric: divide your weight in kilograms by your height in metres squared.

Imperial: multiply weight in pounds by 703, then divide by height in inches squared. This calculator converts imperial inputs for you.