Healthy weight is calculated using a person's height and weight to arrive at a number called body mass index, or BMI. According to the Centers for Disease Control and Prevention, the BMI scale for adults lists a BMI between 18.5 and 24.9 as a normal weight.
A BMI below 18.5 is classified as underweight and a BMI over 24.9 is classified as overweight, according to the CDC. Since many factors, including age and gender, affect the amount of fat, BMI is only used as a guide. For example, a man with a BMI of 22 generally has less fat than a woman with a BMI of 22.