A standard drink of liquor is 1.5 fluid ounces, assuming the spirit is 80 proof (40% alcohol by volume). That’s the amount in a typical shot glass, and it contains roughly 0.6 ounces (14 grams) of pure alcohol, the same amount found in a 12-ounce beer or a 5-ounce glass of wine.
Why 1.5 Ounces Is the Number
The 1.5-ounce figure comes from the way U.S. health authorities define a “standard drink.” Rather than measuring the total liquid, they measure the pure alcohol inside it. One standard drink equals about 14 grams of pure alcohol, regardless of what you’re drinking. A 12-ounce can of regular beer at 5% ABV gets you there. So does 5 ounces of wine at 12% ABV. And so does 1.5 ounces of 80-proof liquor at 40% ABV. The container sizes are different, but the alcohol payload is the same.
This applies to all common distilled spirits: vodka, gin, rum, tequila, whiskey, and bourbon. As long as the bottle says 80 proof or 40% ABV, one shot equals one standard drink.
Higher Proof Spirits Change the Math
Not all liquor is 80 proof. Many whiskeys, rums, and specialty spirits are bottled at 90, 100, or even 120 proof. When the alcohol concentration goes up, the amount of liquid needed to hit one standard drink goes down. For 100-proof spirits (50% ABV), a standard drink is just 1 ounce, not 1.5. That’s noticeably smaller than a typical pour, which means a normal-looking shot of overproof liquor actually contains more than one standard drink.
To figure this out for any bottle, divide the proof in half to get the ABV percentage. A 90-proof bourbon is 45% ABV, so a 1.5-ounce pour contains slightly more than one standard drink. If you’re keeping track of your intake, checking the label matters more than eyeballing the glass.
Cocktails Often Contain Multiple Drinks
A single cocktail frequently holds more alcohol than one standard drink, sometimes significantly more. A classic martini typically uses 2 to 3 ounces of gin or vodka, putting it at roughly 1.5 to 2 standard drinks in one glass. A margarita made with 1.5 ounces of tequila plus an ounce of orange liqueur can land in the same range. A Long Island iced tea, which combines multiple spirits, can contain 3 or more standard drinks despite arriving in a single glass.
Restaurant and bar pours vary too. Many establishments use 2-ounce pours for a “single” cocktail rather than the 1.5 ounces that define a standard drink. A generous home pour can easily be double that. If you’ve ever wondered why two cocktails hit harder than two beers, this is usually the reason.
How Your Body Processes One Drink
The liver breaks down alcohol at a fairly fixed pace: roughly one standard drink per hour for an average-sized adult (around 154 pounds). That rate doesn’t speed up with coffee, food, or water, though food in your stomach can slow how quickly alcohol enters your bloodstream in the first place.
One standard drink raises blood alcohol concentration by approximately 0.01% to 0.03% over an hour, depending on your body weight, sex, hydration, and whether you’ve eaten. For context, the legal driving limit in most U.S. states is 0.08%. A smaller person drinking on an empty stomach will hit that threshold faster than a larger person who just had dinner, even if both consumed the same number of drinks.
What the Guidelines Consider Heavy Drinking
The NIAAA defines heavy drinking as 4 or more drinks on any single day for women, or 8 or more per week. For men, the thresholds are 5 or more drinks in a day, or 15 or more per week. These numbers are based on standard drinks, so accurate counting depends on knowing what a standard drink actually is.
This is where the 1.5-ounce measurement has real practical value. If you pour 3 ounces of whiskey into a tumbler and sip it over an evening, that’s two standard drinks, not one. Two of those tumblers put a woman at the threshold for a heavy drinking day. Knowing the baseline measurement makes it possible to count honestly, which is the entire point of having a standard in the first place.