Like was mentioned there is a serious problem with the "use your fingers around your wrist method" but there is a pretty accurate wrist method that involves a tape measure and your height.
Quote:
Body frame size is determined by a person's wrist circumference in relation to his height.
For example, a man whose height is over 5' 5" and wrist is 6" would fall into the small-boned category.
Determining frame size: To determine the body frame size, measure the wrist with a tape measure and use the following chart to determine whether the person is small, medium, or large boned.
Women:height under 5'2"
small = wrist size less than 5.5"
medium = wrist size 5.5" to 5.75"
large = wrist size over 5.75"
height 5'2" to 5' 5"
small = wrist size less than 6"
medium = wrist size 6" to 6.25"
large = wrist size over 6.25"
height over 5' 5"
small = wrist size less than 6.25"
medium = wrist size 6.25" to 6.5"
large = wrist size over 6.5"
Men:height over 5' 5"
small = wrist size 5.5" to 6.5
"medium = wrist size 6.5" to 7.5"
large = wrist size over 7.5"
Hope this helps (the wrist finger thing doesnt work for me since i have SHORT fingers!!!) I am 5"6.5" and have a 7" wrist so I have a LARGE frame!