Although several classifications and definitions for degrees of obesity are accepted, the most widely accepted classifications are those from the World Health Organization (WHO), based on body mass index (BMI). The WHO designations are as follows:

• Grade 1 overweight (commonly and simply called overweight) - BMI of 25-29.9 kg/m2;
• Grade 2 overweight (commonly called obesity) - BMI of 30-39.9 kg/m2;
• Grade 3 overweight (commonly called severe or morbid obesity) - BMI ≥40 kg/m2.

Some authorities advocate a definition of obesity based on a percentage of body fat, as follows:

• Men: Percentage of body fat greater than 25%, with 21-25% being borderline.
• Women: Percentage of body fat greater than 33%, with 31-33% being borderline.