The designation of “one drink” is based on the standardized amount of pure alcohol it contains, not the size of the glass or the volume of the liquid. Knowing the precise volume is a practical step toward tracking alcohol intake accurately, which is the foundation of recommended consumption limits and health guidelines. This standardization allows for meaningful comparisons across various types of alcoholic beverages, which differ significantly in strength. Health organizations use this uniform measure to communicate safe drinking practices and help individuals monitor their consumption.
Defining the Standard Unit of Alcohol
A standard drink is universally defined by the total quantity of pure ethanol, or alcohol, present in the beverage. In the United States, this standard unit contains 0.6 fluid ounces of pure alcohol, which translates to approximately 14 grams of ethanol. This fixed measurement ensures that a standard drink of beer, wine, or distilled spirits contains the same intoxicating load, regardless of the container size or beverage type.
This measurement is the common baseline for health recommendations, allowing medical professionals to offer clear guidance on consumption levels. In the U.S., 14 grams of ethanol is used because it represents the amount the average liver can process in about one hour. The amount of pure alcohol must be calculated by volume since different drinks have widely varying alcohol concentrations.
The Standard Pour of Wine in Milliliters
The volume of wine required to meet the 14-gram standard is determined by dividing the pure ethanol amount by the wine’s Alcohol By Volume (ABV) percentage. For standard table wine, the ABV is typically around 12%. Applying this calculation, one standard drink of wine is defined as 5 fluid ounces.
Converting 5 fluid ounces to the metric system yields approximately 148 milliliters (ml). This 148 ml volume is the precise measure of wine needed to contain 14 grams of pure ethanol, assuming the wine is 12% alcohol by volume. Therefore, 148 ml is the benchmark volume used by health organizations when discussing wine consumption.
This standard volume helps consumers and restaurants maintain consistency when following health guidelines. It is the accepted volume that provides the equivalent alcohol content of a 12-ounce regular beer (5% ABV) or a 1.5-ounce shot of 80-proof spirits (40% ABV).
How Different Wine Types Change the Calculation
The standard 148 ml measure is based on an average 12% ABV, but the alcohol content of wine can vary substantially, which directly affects the volume of a standard drink. If a wine has a higher ABV, the volume of a standard drink must decrease to maintain the 14-gram ethanol limit. Conversely, a wine with a lower ABV would require a slightly larger volume to meet the same standard.
Adjusting for Alcohol By Volume (ABV)
For example, a wine with a 15% ABV requires a smaller pour of approximately 118 ml to count as one standard drink. Fortified wines, like Port or Sherry, often range from 17% to 20% ABV, reducing the standard drink size to about 88 ml to 103 ml. Conversely, a light white or sparkling wine at 10% ABV would require a volume of about 177 ml to meet the standard.
Real-World Serving Sizes
It is important to contrast the standard 148 ml measure with real-world serving sizes, which can lead to unintentional overconsumption. Many restaurants and home pours often exceed the 5-ounce standard, frequently ranging from 6 to 9 ounces (177 ml to 266 ml). These larger pours count as 1.2 to 1.8 standard drinks. This means a single, generous glass may already represent more than one drink for tracking purposes.