Body mass index

Body mass index, or BMI, is a calculation using weight and height: weight in kilograms divided by height in metres squared. It is used as a broad screening measure, not a diagnosis of an individual's health. It does not directly measure body fat, fitness, nutrition or how fat is distributed.

What can BMI tell me?

Adult BMI categories can help identify when further assessment may be useful, particularly alongside other risk factors. They are population-based screening categories rather than a complete judgement about one person. A clinician may also consider waist measurement, blood pressure, medical history and relevant blood results.

The calculation has limitations for people with high muscle mass, pregnancy, some disabilities and certain other circumstances. Children and teenagers need age-appropriate interpretation rather than the standard adult categories. Different populations may have different risk patterns at the same BMI.

For the Australian guidance behind this explanation, see Healthdirect Australia: Body mass index (BMI) and waist circumference - Healthdirect Australia.

How should I use a calculator result?

Check units and measurements, then treat the result as one starting point for discussion. A small change in height entry can affect the calculation. Do not use a category alone to decide that you need treatment or that symptoms can be ignored.

If weighing or tracking numbers causes distress, tell the clinician. Health goals can include function, eating patterns, sleep and metabolic health rather than only a target weight. A doctor can explain which measures are useful for your circumstances.

Does a higher BMI guarantee illness?

No. Risk and diagnosis are different concepts, and people within any category can have health concerns. Equally, a result in a commonly described healthy range does not rule out disease. Assessment should remain individual and respectful.

Explore Doccio's calculators and weight-management service information. A calculator cannot decide whether a prescription or programme is appropriate. A clinician considers the broader picture, and no particular weight-loss result should be promised from a BMI value.

Where to go next

Read Doccio information about weight management to understand the relevant service. A doctor decides whether a consultation, examination, referral or another pathway is appropriate for your situation.