A finger of a beverage varies with each individual and the diameter of the container. It is generally accepted as the amount of liquid one must remove (usually by drinking) to lower the level of the liquid by the width of one finger. The finger used is normally the index, middle or thumb. Finger measurements are commonly used in drinking games as a convenient and simple way of ensuring that those who take penalty drinks receive a suitably-sized quantity of their drink.
Narcotics
Street narcotics, especially heroin, are sometimes sold by the "finger," an amount equaling approximately 10 grams.
