The most frequently used measure of being over-weight or obese is based on the body mass index (BMI). The BMI is defined as weight/ heighy2 (with weight in kilograms and height in metres). Adults with a BMI between 25 and 30 are defined as overweight and those with a BMI over 30 as obese. This classification may not be suitable for all ethnic groups and adult thresholds are not suitable for children.
For most countries, estimates of overweight and obesity rates are based on self-reports of height and weigh from health interview surveys.