BMI is a measurement of nutritional status, calculated as an individual's weight (in kg) divided by his or her height (in meters squared). In adults, a value below 18.5 indicates chronic energy deficiency or thinness. A BMI between 18.5 and 24.9 is considered a healthy weight, a BMI of 25 to 29.9 is considered overweight, and a BMI of 30 or greater is classified as obese. These cut-offs have been used to assess nutritional status of individuals 18 years of age and above, and females 15 years of age and above. In children, overweight is identified using comparisons of BMI-for-age against standard reference populations.
Source: FANTA 2018 - https://www.fantaproject.org/tools/anthropometry-guide