Obesity is defined as having a body mass index (BMI) of greater than or equal to 30 kilograms per meters squared (kg/m2; “meters” meaning a person’s height). More specifically, a person with:[1]
- A BMI of 25 to 29.9 is “overweight”
- A BMI of 30 to 34.9 has “class I obesity”
- A BMI of 35 to 39.9 has “class II obesity”
- And a BMI of 40 or higher has “class III obesity”
While BMI is a generally useful measurement at the population level, because it only accounts for total body mass, individuals who are tall and/or muscular may have a BMI that qualifies as “obese”. As such, it’s useful to factor other measures like body fat percentage into an evaluation of whether someone has obesity.[2]