Many different body shapes and sizes are healthy, so you won't find a single calculation to tell you exactly what you should weigh and what your measurements should be. You can use several calculations and measurements, however, to determine whether you're within the acceptable range for ideal body size: ideal body weight, BMI, waist circumference and waist-to-hip ratio. These numbers are typically used to assess body fat and determine potential health risks related to body size.
Calculating Ideal Body Weight
A simple calculation can give you an idea as to your ideal body weight, or IBW. Start with 100 pounds for the first 5 feet of height; then add another 5 pounds for each inch over 5 feet. If you're under 5 feet, subtract 2 pounds for each inch under this height. This gives you the ideal body weight for a woman with a medium frame. For example, the IBW for a woman who is 5 feet, 6 inches tall is calculated like this: 100 + (5 x 6) = 130 pounds.
Frame size also plays a role in determining IBW. Someone with a small frame may have a weight at the low end of the acceptable range, while someone with a large frame could have a weight near the high end of this range. A quick way to estimate your frame size is to wrap your thumb and middle finger around your wrist. If the fingers just touch, you have a medium frame. Should your fingers overlap, you have a small frame, and if your fingers don't touch at all, you have a large frame.
If you have a small frame, subtract 10 percent from the ideal body weight, and if you have a large frame, add 10 percent. So, using the example IBW of 130, can subtract and add 10 percent, or 13 pounds, to find the ideal body weight range for a 5-foot, 6-inch-tall woman: 117 to 143 pounds.
Healthy Weight Ranges Using BMI
Of course, more than one weight is healthy for any given height. Doctors typically use body mass index as a screening tool to determine whether a woman is at an acceptable weight and body fat level. To determine if your weight falls within the healthy range, you can use an online BMI calculator to get your BMI. Put your height and weight into the calculator, and if the result falls between 18.5 and 24.9, you're at a healthy weight for your height. A BMI less than 18.5 indicates you're underweight, and a number 25 or higher shows that you're overweight. For example, a 5-foot, 6-inch-tall woman who weighs 140 pounds has a BMI of 22.6, which is within the normal range.
Taking Waist Circumference Into Account
The ideal body weight equation and BMI don't take into account your body composition. Carrying too much weight in the abdominal area increases your risk for health problems, such as diabetes, gallbladder issues, breast cancer and heart disease, because it indicates you have a dangerous type of fat, called "visceral fat," around your organs.
Take your waist measurement at your natural waist, which is between your belly button and the bottom of your ribs where your torso is narrowest. Place the tape directly against the skin for the most accurate measurement. As a woman, your waist circumference should be less than 35 inches.
Another measurement that can help you figure out if you're proportioned properly for good health is the waist-to-hip ratio, or WHR. If waist circumference divided by hip circumference is less than 0.8, you have a "pear" shape. A WHR higher than 0.8 indicates you have an "apple" shape, which is a sign you may have excess visceral fat in your abdomen.
For your hip circumference, measure around your hips at their widest point. If you're not sure exactly where that is, take a few different measurements and use the highest number.
Body Fat Considerations
Use a combination of these different calculations to provide an idea of how close you are to your ideal body size. Some women have a BMI that falls within the recommended range but have more body fat than is healthy. If you have a normal BMI, but your waist circumference is larger than 35 inches, you may have what's called "normal weight obesity." This condition poses the same risks as being overweight, including a higher likelihood of developing type 2 diabetes and heart disease.
If you're concerned you may have too much or too little body fat, your doctor can have your body fat measured to see if it's within the acceptable range for women of 14 to 31 percent. Some gyms and health clubs also offer this service to their members.