Body Mass Index (BMI) is the standard criteria for determining whether you have a healthy body weight or not. It is measured with respect to an individual’s weight and height. It is totally independent of age and the values are same for both men and women.
In case of children it is calculated relative to age and sex, while in adults read by standard weight values which are equal for every age for both sexes. Body weight within the range of 18.5 and 25 is considered to be a healthy body weight. A Body Mass index of low range is termed as underweight and a higher BMI is considered as overweight. Any person having BMI beyond the health range is posed to some high health risks.
It can be measured using BMI calculators or BMI charts. It does not measure the amount of fat in body directly which is why should not be determined as the only criteria for diagnosing any health risk.