There are a lot of ways to measure fitness. One of them by the weight and height of an individual or BMI (Body mass index).

BMI (Body mass index)

BMI is a measurement of an individual’s leanness or chubbiness established on their length and mass and is aimed at quantifying tissue mass. It is widely used as a common indicator of whether an individual has a decent body weight for their length. Mainly, the value collected from the calculation of BMI is used to categorize whether an individual is underweight, normal weight, overweight, or obese relying on what range the integrity falls between. These spectra of BMI vary based on components like region and age and are periodically further halved into subcategories like severely underweight or very severely obese. Being overweight or underweight can have substantial health effects and risk so while BMI is an inadequate measure of healthy body weight, it is a helpful indicator of whether any more testing or action is needed

BMI can be calculated by using formula

BMI= weight in kg/ (height in inches) 2

BMI =
mass (kg)
height2 (m)

 

Value of any individual above age 18 should have

Category BMI range – kg/m2
Severe Thinness     < 16
Moderate Thinness  16 – 17
Mild Thinness  17 – 18.5
Normal  18.5 – 25
Overweight  25 – 30
Obese Class I  30 – 35
Obese Class II  35 – 40
Obese Class III  > 40

 

Or more information about BMI respect to the country. https://www.who.int/data/gho/data/themes/topics/topic-details/GHO/mean-body-mass-index-trends-age-standardized-(kg-m-)

However, BMI is a good way to measure fitness but it does not give information related to your fat and muscles so it can be the wrong indication for someone for those who have a high amount of muscles as well as for old age people and girls they have more fat than other in most of the conditions.

BMI is just an estimate that doesn’t take body composition into account because of many variations or different from each other as well as muscle distribution, bone mass, and fat, BMI all these should be considered with other criteria rather than being used as the main method for determining individual healthy body weight.