Researchers use an estimate of an individual's relative fat and muscle mass, called body mass index, to define obesity. To find your BMI, check out this calculator.
Adults with a BMI of between 25 and 30 are considered overweight. Those with a BMI over 30 are obese.
Morbid obesity applies to adults with a BMI over 40 or who are more than 100 pounds overweight.
Source: The National Library of Medicine.