A standard drink in the United States contains roughly 17.7 ml of pure alcohol. That number comes from the official definition set by the National Institute on Alcohol Abuse and Alcoholism (NIAAA): one standard drink equals about 14 grams, or 0.6 fluid ounces, of pure ethanol. Since pure ethanol has a density of about 0.789 grams per milliliter, 14 grams works out to approximately 17.7 ml.
Where 17.7 ml Comes From
Alcohol is measured by weight (grams) in most health guidelines, but many people think in terms of volume. The conversion is straightforward: divide the 14 grams by ethanol’s density (0.789 g/ml) and you get about 17.7 ml of pure liquid alcohol. That’s the amount of actual ethanol in every standard drink, regardless of whether it arrives in a beer can, a wine glass, or a shot glass.
You can also calculate the pure alcohol in any beverage yourself. Multiply the drink’s total volume in milliliters by its ABV (alcohol by volume) as a decimal. A 355 ml can of 5% beer, for example: 355 × 0.05 = 17.75 ml of pure alcohol. That lines up almost perfectly with the standard drink definition, which is exactly why those serving sizes were chosen.
How It Looks in Common Drinks
The three classic examples of a standard drink each deliver the same ~17.7 ml of ethanol in different packages:
- Beer (5% ABV): 12 oz (355 ml). Multiply 355 × 0.05 = 17.75 ml of pure alcohol.
- Wine (12% ABV): 5 oz (148 ml). Multiply 148 × 0.12 = 17.76 ml of pure alcohol.
- Distilled spirits (40% ABV / 80 proof): 1.5 oz (44 ml). Multiply 44 × 0.40 = 17.6 ml of pure alcohol.
The math is simple, but it only works when the ABV matches those standard percentages. Many craft beers run 7 to 9% ABV, which means a single 355 ml can could contain 25 to 32 ml of pure alcohol, nearly two standard drinks. Similarly, wines frequently land between 13.5% and 15%, pushing a regular glass well past one standard drink.
Standard Drinks Vary by Country
The 14-gram (17.7 ml) definition is specific to the United States. Other countries draw the line differently. The UK sets a “unit” at 8 grams (about 10 ml of pure alcohol). Australia defines a standard drink as 10 grams (roughly 12.7 ml). Japan uses 19.75 grams (about 25 ml), and Austria sets its standard at 20 grams (roughly 25.3 ml). If you’re reading health guidelines from another country, the number of “drinks” they recommend won’t translate directly to U.S. standards.
Why Real-World Pours Rarely Match
The standard drink is a measurement tool, not a description of what actually ends up in your glass. Restaurant and bar wine pours in the U.S. commonly run 6 ounces rather than 5, and some places offer 8 or 9 ounce options. A 6-ounce pour of 14% wine contains about 25 ml of pure alcohol, roughly 1.4 standard drinks. Bartenders also vary on spirit pours, and many cocktails contain two or more shots.
Home pours tend to be even more generous. Studies on self-pouring consistently find that people overshoot a standard serving, especially with wine and spirits. If you’re trying to track your intake accurately, measuring with a jigger or checking the total volume of the bottle against the number of glasses you get from it gives you a much more realistic count.
How Fast Your Body Processes It
Your liver clears roughly 7 grams of alcohol per hour, which is about half a standard drink. For a person weighing around 70 kg (154 lbs), that translates to a full standard drink taking roughly two hours to metabolize completely. The common shorthand of “one drink per hour” underestimates how long alcohol actually stays in your system. Drinking faster than your liver can process means blood alcohol levels keep climbing with each additional drink.
This rate is relatively fixed. Food, water, and coffee don’t speed up the liver’s processing. They may affect how quickly alcohol is absorbed into the bloodstream, but the actual breakdown rate stays largely the same regardless of what else you consume.
Using the Number to Track Intake
The most practical use of knowing the 17.7 ml figure is being able to calculate the real number of standard drinks in anything you’re served. The formula again: volume in ml × ABV (as a decimal) ÷ 17.7 = number of standard drinks. A 500 ml pint of 6.5% IPA works out to 500 × 0.065 ÷ 17.7 = 1.84 standard drinks. A 250 ml glass of 14% red wine: 250 × 0.14 ÷ 17.7 = 1.98, essentially two full standard drinks in what looks like a single glass.
The 2025-2030 U.S. Dietary Guidelines removed specific numerical limits on alcohol consumption, opting instead for a general recommendation to “consume less alcohol for better overall health.” Previous editions had suggested up to one drink per day for women and two for men. Regardless of where guidelines land, knowing how to count what you’re actually drinking is the foundation for any informed decision about alcohol.