Both body mass index (BMI) and waist circumference can be used to measure obesity. Due to its ease of measurement, waist circumference alone is favoured over measurement of the waist:hip ratio. Either BMI or waist circumference can be used alone, however the WHO recommends determining the BMI, where possible, and using it in combination with waist measurement1.
Body Mass Index is a measure of whether you are a healthy weight for your height. A person with a BMI of between 18.5 -24.9 is considered to be a healthy weight for their height and in the healthy range. A person with a BMI over 25 is considered overweight, while a person with a BMI of 30 or more is considered obese. Obesity puts people at a raised risk of developing health problems such as heart disease, stroke, and type 2 diabetes2 - in fact, one study has estimated that, among US women with a BMI greater than 29kg/m2, 53% of deaths could be directly related to their obesity3.
Body Mass Index is a person’s weight in kilograms divided by the square of their height in metres.
BMI = weight (kg) / height² (in m)
Measure the waist circumference at the end of several consecutive natural breaths, at a level parallel to the floor, midpoint between the top of the iliac crest (hip bone) and the lower margin of the last palpable rib in the midaxillary line (the side of the body, directly below the underarm).
Make the measurement with a stretch‐resistant tape that is wrapped snugly around the subject, but not to the point that the tape is constricting. Keep the tape level and parallel to the floor at the point of measurement.
|Body mass index||Obesity class||Disease risk (relative to normal weight and waist circumference)|
|Men < 40 in (102 cm)
Women < 34 in (88 cm)
|Men > 40 in (102 cm)
Women > 34in (88 cm)
|Extreme obesity||>40.0||III||Extremely high||Extremely high|