Body Mass Index
According to the Centers for Disease Control and Prevention, BMI (Body Mass Index) is a reliable way of determining your healthy weight. A normal BMI is between 18.5 and 24.9. Using the CDC BMI calculator, an average weight for a woman who is 5 feet 8 inches is between 122 and 164 lbs.
Just because you fall out of the normal BMI range doesn't necessarily mean you're underweight or obese. If you worry about either of these possibilities, a doctor's visit is the best way to determine the ideal weight for you and your health. A doctor is able to take into account individual variables, such as medical history.
For most women, maintaining a healthy BMI will keep them in their ideal weight range. If you want a personalized opinion, however, speak with your doctor about your weight.