The term “a fifth” is a common, historical measurement referring to a specific size of liquor bottle used in the United States. To accurately determine the number of drinks a fifth of vodka contains, standardized measurements must be applied. This calculation requires defining the bottle’s volume and correlating it with the official definition of a standard alcoholic drink.
Defining the Volume of a Fifth
The term “fifth” is a vestige of a time when spirits were bottled in containers that held one-fifth of a US liquid gallon. Today, this volume is universally standardized as the 750 milliliter (mL) bottle size. This metric measurement is the standard capacity for most spirits and wines worldwide, despite the old name persisting. A fifth holds approximately 25.4 fluid ounces of liquid.
The calculation of standard drinks must also consider the alcohol concentration of the vodka itself. Most vodka sold is 80 proof, which translates to 40% Alcohol by Volume (ABV). Brands also commonly offer higher-proof options, such as 100 proof (50% ABV). This variation in alcohol content significantly alters the total number of standard drinks within the bottle.
What Constitutes a Standard Alcoholic Drink?
To measure alcohol content consistently, health organizations in the United States define a “standard drink.” This definition is based on the quantity of pure ethanol, not the volume of the beverage itself. Specifically, one standard drink contains 0.6 fluid ounces of pure alcohol.
This pure alcohol measurement sets the equivalent serving sizes for different types of alcoholic beverages. For distilled spirits, typically 80 proof (40% ABV), the volume containing 0.6 ounces of pure alcohol is 1.5 fluid ounces. Therefore, a 1.5-ounce pour of 80-proof vodka is considered one standard drink. This allows for a comparison of alcohol consumption across different types of drinks.
Calculating the Total Standard Drinks
The number of standard drinks in a fifth of vodka is determined by dividing the total bottle volume by the volume of a single standard drink. For the most common variety, 80-proof (40% ABV) vodka, a standard drink is 1.5 fluid ounces. Since a fifth contains approximately 25.4 fluid ounces, the calculation is 25.4 ounces divided by 1.5 ounces per standard drink.
Performing this math reveals that a fifth of 80-proof vodka contains approximately 16.9 standard drinks. The 750 mL bottle size contains 17 servings when rounded to the nearest whole number.
The total count changes for higher-proof spirits because a smaller volume is needed to reach 0.6 ounces of pure alcohol. For 100-proof vodka (50% ABV), one standard drink is only 1.2 fluid ounces. Dividing the 25.4-ounce bottle size by 1.2 ounces per standard drink yields approximately 21.1 standard drinks.