Originally a bar measuring tool, ( and still used as one) , the shot glass has become the choice for "shots" of spirits. Also known as a "jigger", especially as a measuring tool. Tthe shot glass usually holds between 1oz and 2ozs.
Traditionally, a shot glass was a small, thick glass designed to measure one ounce of liquid, usually liquor, to be either drunk straight, or poured into a mixed drink. Markings, if any, indicated the quantity of fluid at different levels.