A standard shot is 1.5 ounces of liquid. However, in many alcoholic mixed drinks, 1.25 ounces of hard liquor is considered a shot. A shot of espresso is often considered to be 1 ounce.
The use of a shot is not standardized across all beverage applications. When used with alcoholic drinks, 1.5 ounces is the general standard and is equivalent to the alcohol in a 12-ounce can of regular beer or a 5-ounce pour of wine. When used with coffee, a standard shot can be more or less than 1 ounce due to brewing practices but is generally 1 ounce.