What Does The Proof Of Alcohol Mean And How Is It Related To ABV?

When shopping for spirits, you might see two different values on labels: "ABV," or alcohol by volume, and "proof." That second one isn't always there, as distilleries in the United States aren't required to list it these days. But when it is, it can be confusing. Most of us know ABV and that it tells us how much alcohol is in a beverage — we see it on beer and wine. But what does that proof number mean?

Proof also refers to the amount of alcohol present, and in the U.S., it's calculated by doubling the ABV. So, if a spirit is 40% ABV, it's 80 proof. ABV is straightforward: It measures how many milliliters of pure ethanol (or alcohol) are in every 3.4 ounces of fluid. Distillers use hydrometers to measure spirits through each stage of the distilling process. The proof has a looser, more storied background. England demanded a tax on spirits with high levels of alcohol in the 16th century, testers would soak a pellet filled with gunpowder in liquor before attempting to ignite it — if it burst into flames, the alcohol level was high enough for it to be deemed a proof spirit. When setting its own taxation standards, the U.S. decided "proof spirits" were anything over 50% ABV, which would correspond with 100 proof. Restrictions changed, but proof equaling double ABV was set — for America, at least; the correlation differs in other countries.

While ABV is more important on the consumer side — it's the one that legally must be printed on distilled spirits' bottles, and the one the average imbiber knows. But distillers use proof to guide their process, and to make sure they're producing spirits that fit into their categories. For example, one of the things that distinguishes the difference between bourbon and whiskey is bourbon must be distilled to no more than 160 proof and bottled at 80 proof or higher. Bourbon's proof increases during its mandated barrel-aging period, and so it — like other spirits — gets carefully proofed down with just the right amount of water.

All spirits count proof among the factors that classify them. Proof doesn't factor into beverages like beer, hard seltzer, ready-to-drink cocktails, or wine, even when it's fortified wine, made stronger with a spirit. These categories' ABVs never get high enough that the government considers them "proof spirits" to begin with. Of those, there are the different types of brandy, at 35% to 60% ABV, so 70 to 120 proof. Moving higher in proofs, there's gin, 40% to 55% ABV, so 80 to 110 proof; then there are the various kinds of rum at around 40% ABV or 80 proof. Whiskey can weigh in from 40% to 50% ABV or 80 to 100 proof. Tequila also ranges from 40% to 55% ABV and 80 to 110 proof and vodka runs 40% to 90% ABV, so 80 to 180 proof.