Diagnosis of Obesity Body mass index (BMI) Waist circumference Sometimes body composition analysis In adults, BMI, defined as weight (kg) divided by the square of the height (m 2), is used to screen for overweight or obesity (see table Body Mass Index): Overweight = 25 to 29.9 kg / m 2 Obesity = ≥ 30 kg / m 2 However, BMI is a crude screening tool and has limitations in many subpopulations.