There are several ways to calculate your body frame size. One of the simplest is to wrap the thumb and the longest finger of one hand around the wrist of the other hand, being sure to measure at the narrowest point. If your fingers touch or overlap, you're small framed. If your fingers don't touch and there's a space between them, you're large framed. In some cases, you might want to use a more exact method in order to calculate your frame and ideal weight, however.
To measure body frame more exactly, you will need a tape measure, a pad and pencil to write your measurements down, and perhaps a friend to help you hold the tape measure. First, measure your wrist, writing down the number. Then measure your exact height. You will need to enter these numbers into a chart in order to calculate the ideal weight for your height and frame size.
For a woman under 5 feet 2 inches (157.48 cm), a wrist size smaller than 5.5 inches (13.97 cm) indicates a small body frame. A measurement of 5.5 inches to 5.75 inches (13.97 to 14.61 cm) indicates a medium frame, and a wrist size larger than this indicates a large frame. Women 5 feet 2 inches to 5 feet 5 inches (157.48 to 165.1 cm) in height, a wrist size smaller than 6 inches (15.24 cm) is small, 6 inches to 6.25 inches (15.24 to 15.875 cm) is medium, and over this size is large. For a woman over 5 feet 5 inches (165.1 cm), a wrist size smaller than 6.25 inches (15.875 cm) is small, 6.25 inches to 6.5 inches (15.875 to 16.51 cm) is medium, and a measurement higher than this is large.
The body frame size measurements for men take into account fewer variations. For a man whose height is over 5 feet 5 inches (165.1 cm), a wrist size of 5.5 inches to 6.5 inches (13.97 to 16.51 cm) indicates a small frame. A medium frame has a measurement of 6.5 inches to 7.5 inches (16.51 to 19.5 cm), and anything higher is considered large.
Once you have your frame size, you can plug the numbers into a body size chart to calculate your goal weight for your frame type. Many pre-written charts can also be found on the Internet on health websites or weight loss forums, allowing you to skip the calculator.
The body frame measurement came about in the 1940s and '50s though the efforts of the Metropolitan Life Insurance Co. Their goal was to find a way to measure whether someone was obese in order to calculate the risk of giving them a life insurance policy. For decades, this practice was used to determine a person's healthy weight, but it was not clear if this method was reliable. When the body frame tables were originally worked out, the sample size was small, and did not take into account the frame differences between races.
More recently, the Body Mass Index (BMI) is seen as a more reliable way to determine one's goal weight. The BMI takes into account a person's weight and height, and leaves out wrist measurements altogether. There is still some debate over whether BMI is an accurate measure of overall health, however.