BMI Calculator

What your BMI result means

Body Mass Index (BMI) compares your weight with your height. It is a quick screening number that doctors and public-health bodies use to flag whether weight may be affecting health risk. It is a starting point, not a diagnosis.

The formula

BMI = weight (kg) ÷ height (m)². In pounds and inches: BMI = 703 × weight (lb) ÷ height (in)².

Worked example

A person who weighs 70 kg and is 1.75 m tall has BMI = 70 ÷ (1.75 × 1.75) = 70 ÷ 3.0625 = 22.9, which falls in the normal range.

WHO adult categories

• Below 18.5: underweight
• 18.5 to 24.9: normal weight
• 25.0 to 29.9: overweight
• 30.0 and above: obese

Some health bodies recommend lower cut-offs for South Asian adults, for example treating 23 and above as increased risk, because health risks can rise at lower BMI in these populations.

Limitations to keep in mind

• BMI does not separate muscle from fat, so athletes and very muscular people can be classed as overweight.
• It ignores where fat is stored. Waist circumference is a useful extra measure.
• It is not designed for children, teenagers, pregnant women or older adults, who have different reference charts.

If your result is outside the normal range or you are worried about your weight, speak to a doctor or registered dietitian. This tool is for information only.

Frequently asked questions

Is a normal BMI always healthy?

Not necessarily. Diet quality, activity, sleep and family history all matter, and a normal BMI does not rule out health problems.