When you select an item that requires you to select from available sizes, a sizing chart will be displayed. Use the following to determine your size.
How to measure information for men and women
Measure the circumference of you head using a cloth measuring tape. Start approximately 1" above your eyebrows in front and go completely around to the largest point at the back of the head.
Place your arms loosely at your sides. Measure slightly below armpits, completely around the back and across the broadest part of the chest.
Take a shirt that fits you very well and lay the collar flat. Measure from the center of the collar button to the far end of the button hole. The number you come up with is your neck size.
Measure from the center of the collar (in back), across the shoulder and down the sleeve. This is your sleeve length.
With heels together, measure completely around the fullest part of the hips.
Wear the shoes that you would normally wear with the style of pants you are purchasing. Measure from well up into the crotch area to the point on the foot to the required length.
Here you can find more Manufacture Sizing Charts