Body Mass Index (BMI)

Body mass index (BMI) measures the relationship between your weight and your height. Although this tool has been embraced internationally as an assessment tool for health risks, based on recommendations of the World Health Organization, it has its limitations.

For example, if you carry excess weight for your height, your BMI number will not indicate whether the excess weight consists of lean muscle mass or fat mass; therefore, the health risks associated with your BMI may be underestimated or overestimated.

This is why a BMI assessment should be part of a comprehensive health assessment. It will not accurately calculate your health risks if you are:

  • a muscular athlete

  • under age 18 and have not reached full growth

  • a pregnant or lactating woman

  • over the age of 65 years

BMI Calculator





BMI Categories and Health Risks

Underweight: less than 18.5 — increased health risk

• Severe thinness: less than 16.0

• Moderate thinness: 16.0 – 16.9

• Mild thinness: 17.0 – 18.4

Normal range: 18.5 – 24.9

Overweight: 25.0 – 29.9 — increased health risk

Obese: 30.0 or higher

• Obese class I: 30.0 – 34.9 — high risk

• Obese class II: 35.0 – 39.9 — very high risk

• Obese class III: 40.0 or higher — extremely high risk

Waist Circumference

Your waist circumference provides additional information regarding exposure to health risks. A circumference higher than 88 cm (35 inches) for women and 102 cm (40 inches) for men increases risk.

However, if your waist circumference is lower than those cut-off points, you are not necessarily in the clear if your BMI exceeds 25 kg/m². Similarly, you may be at risk for health disease if your waist circumference exceeds the cut-off points even if you are of normal weight.

Women: 88 cm (35 inches)

Men: 102 cm (40 inches)

Measuring Your Waist

  • Your waist is measured midway between your last rib and the top of your iliac crest (hip bone).

  • Measurements should be taken on bare skin.

  • Find the point at the top of your hip bone. Place the tape around your waist with the lower edge of the tape at that point.

  • Use a cross-handed technique so that the zero mark on the tape crosses the measure on the tape. Ensure the tape is parallel to the floor.

  • Ensure the tape is snug, but not too tight.

  • Exhale, then read the measure at the end of a normal expiration.

References

World Health Organization. (1995). Physical status: The use and interpretation of anthropometry. Report of a WHO Expert Committee. WHO Technical Report Series 854. Geneva, Switzerland: World Health Organization.

WHO Expert Consultation. (2004). Appropriate body-mass index for Asian populations and its implications for policy and intervention strategies. The Lancet, 363(9403), 157–163.