Being a normal weight for your height is one of the best things you can do for both your general health and your fertility. With bodies that come in different shapes and sizes, it can be difficult to know exactly how much you should weigh in order to be considered healthy. BMI, or body mass index, is one way of evaluating your weight. This metric applies to both men and women and is used by health professionals in order to determine if a person is underweight, normal weight, overweight or obese. While there are a number of online calculators that can assist with determining this information, knowing how to calculate your BMI manually can help you stay focused on your health and fitness goals.