Many health professionals and national organizations use the body mass index, or BMI, as a guide for normal weight. You can use BMI as an indicator of body fat, and also as a way to assess weight status. The BMI formula is the same regardless of gender, and its purpose is to make up for the effects of height when evaluating a person's weight.
BMI Calculation
The formula for BMI divides weight, in kilograms, by the square of height, in meters. If you use the American system of pounds for weight and inches for height, you can use the same formula and multiply by 703. To calculate the weight at a certain BMI for a woman at 5'8", change the formula around so that weight in pounds equals BMI times the square of the height in inches times the reciprocal of 703.
Normal Weight
The Centers for Disease Control and Prevention categorizes a BMI of 18.5 to 24.9 as normal. You can find out the weight range, in pounds, that this BMI range corresponds to by using the formula. For a BMI of 18.5, the weight for a woman with a height of 5'8", or 68 inches, is 18.5 times 68 times 68 times 1/703, or 122 pounds. You can use the same formula to find that a BMI of 24.9 means a weight of 164 pounds. This puts a normal weight range for a 5'8" woman at between 122 and 164 pounds.
Overweight and Obesity
Based on BMI, the Centers for Disease Control and Prevention gives a range of 122 to 164 pounds as the normal weight range for a woman of height 5'8". However, about two-thirds of Americans fall above the cut-off of a BMI of 24.9. Those with a BMI between 24.9 and 30 are overweight, and a BMI over 30 means obese. The formula for BMI shows that a woman who is 5'8" tall is obese if she weighs 197 pounds or more.
Interpretations
The CDC has divided BMI values into weight status categories of underweight, normal weight, overweight, and obese, with the idea that having a BMI in the normal weight category means having the lowest health risk. Risks of being underweight include osteoporosis and low body fat, and risks of being overweight include high cholesterol, high blood pressure, osteoarthritis and type 2 diabetes. A woman who is 5'8" should be aware of these implications when assessing her weight.
Considerations
The BMI provides a rough assessment of body fat and likely health status, but other factors influence what a normal weight for a woman who is 5'8" tall should be. Strong athletes may have high amounts of muscle, very low body fat percentages, and high weights and BMIs. Despite having a high weight, these athletes are not at high risk for health problems that a high body fat percentage might cause. Similarly, a 5'8" woman who is within the range of 122 to 164 pounds may be susceptible to health risks if she does not exercise, and instead has a high body fat percentage despite having a normal weight.
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