Before potential weight loss surgery patients are approved for the surgery, they must qualify. The qualifications generally state that a person should weigh 100 pounds over their ideal body weight or should have a body mass index of 40 or more. Those that are 80 pounds overweight are often considered for the surgery if they have health related issues that are linked to obesity.

It is important for a doctor to assess each potential surgery patient individually because measuring obesity can be subjective.
For example, when calculating the ideal weight or the body mass index, these often do not take into consideration muscle mass. Because muscle weighs more than fat, a very muscular person may rate high on the body mass index chart, but not be overweight. In addition, patients that are suffering from illnesses such as type 2 diabetes, hypertension or high blood pressure or sleep apnea and are overweight can be considered as a good candidate for the surgery.

The body mass index is often used to calculate the risks of obesity. This is the most common form of body weight and obesity measurement. The body mass indeed is the body weight in kilograms divided by the square of the height in meters. This can also be measured using pounds and inches. The body mass index does not actually measure body fat, but is generally accepted as an acceptable correlation to the degree of obesity. The index is used when determining obesity, but is not used as a measurement alone.

In 1998, the National Institute of Health adopted standards to help health care professionals measure obesity. These standards help doctors and professionals from all over the United States accurately measure obesity.
The ideal body mass index rating for most people is considered 19 to 25. These are usually people of average height and weight. A person who is much taller can weight more, but not be overweight. That is why it is important for health care professionals to have a standard to go by when determining whether or not a person should or should not have weight loss surgery.

In order to qualify for weight loss surgery, a patient should be considered morbidly obese. Sometimes severely obese people are considered for this surgery if they present health issues.

• A patient with a body mass index of 25 to 29.9 is considered overweight.
• Those with a body mass index of 30 to 34.9 are considered obese.
• A severely obese patient is one with a body mass index of 35 to 39.9.
• A morbidly obese patient will have a body mass index of 40 and over.

Another common measurement of obesity is the waist circumference test. This measurement is often used in conjunction with other measurements and methods.
Along with the body mass index chart, this is usually an accurate measurement of obesity.
   - A man with a waist greater than 40 and a woman with a waist great than 35, show an increase risk for obesity.
Doctors often use combined methods to measure obesity.