Obesity is usually measured in terms of Body Mass Index (BMI).

Obesity can be classified as:
- mild or class 1 obesity (BMI = 30-34.9; 20-40% excess weight)
- moderate or class 2 obesity (BMI = 35-39.9; 41-100% excess weight)
- severe or class 3 obesity or morbid obesity (BMI = >40; 100% excess weight).

In Italy, according to data collected in 2010 by the Istituto Superiore di Sanità (Superior Health Institute), 32% of adults are overweight while 11% are obese (BMI > 30 kg/m²); morbid obesity (BMI > 40 kg/m²) is found in approximately 0.8 - 1% of the population.


Obesity is also classified into two types, based on the distribution of adipose tissue, i.e. localization of the excess fat:

- abdominal obesity, also known as visceral or android obesity: this is characterized by excessive body fat around the stomach and abdomen. This form is commonly known as “apple shape” obesity. Central obesity is associated with metabolic disorders (such as diabetes and dyslipidaemia) and cardiovascular diseases (such as hypertension, atherosclerosis and cardiopathy).

- peripheral obesity also known as subcutaneous or gynoid obesity: this is when fat accumulates mainly at a subcutaneous level, particularly in the buttocks, lower back region as well as in the hips and thighs and the abdomen region below the navel. It is commonly defined as "pear-shape" obesity.

- there are also forms of obesity known as overall or mixed-type obesity which make up the most common forms of obesity especially in those classes characterized by a higher body mass index. This consists in a uniform increase in adipose tissue all over the body, both visceral and subcutaneous.

Overweight            25-29.9
Class I obesity        30-34,9
Class II obesity       35-39.9
Class III obesity      > 40