What is BMI?

Body Mass Index is a screening measure calculated from weight and height. It can help provide a broad starting point, but it does not directly measure body fat or overall health.

Adult BMI reference ranges

• Below 18.5: underweight range
• 18.5 to 24.9: healthy weight range
• 25.0 to 29.9: overweight range
• 30.0 and above: obesity range

These categories are commonly used for adults and may not apply to children, teenagers, pregnant people or all ethnic groups. Muscle mass, age and other health factors matter.

Worked example: 70 kg and 175 cm

Convert 175 cm to 1.75 metres. Square the height: 1.75 × 1.75 = 3.0625. Divide 70 by 3.0625 to get a BMI of approximately 22.9. This falls within the usual adult healthy-weight reference range of 18.5 to below 25.

The standard adult categories apply to adults aged 20 and older. BMI is a screening measure, not a diagnosis, and it does not directly measure body fat. Read the CDC adult BMI category guidance and discuss personal results with a healthcare professional.

Frequently asked questions

Is BMI a diagnosis? No. BMI is a screening measure and should be interpreted with other health information by a qualified healthcare professional.

What units does this tool use? Enter weight in kilograms and height in centimetres.

Health disclaimer: This calculator is for general educational information only. It is not a substitute for professional medical advice, diagnosis or treatment.

Related guide: How to calculate BMI explains the formula, adult ranges and limitations.