How to Convert Proof to Percentage

There’s no simple way of converting alcohol percentage to proof or proof to percentage. Pouring your favorite scotch in the United Kingdom means drinking a different proof of alcohol than if you were drinking it in France. And in the United States, it’s another number. It’s still the same scotch, the same alcohol by volume (ABV), but different proofs. Yup. The proof isn’t in the pudding. But it’s close. And why do we calculate alcohol by volume and proof? It’s all about taxes. Distillers pay tax on the spirit based on the proof inside the bottle. The higher the proof, the higher the tax.

Moonshiners and rum runners didn’t come into their careers by accident. They were trying to outrun the tax man and avoid paying the government what amounted to a hefty tax on each bottle. Back in the 1600s, legitimate distillers were tasked with “proving” the alcohol content of their spirit by burning gunpowder in the liquid.

A parcel of gunpowder soaked in a spirit that burned brightly and cleanly when set on fire would be labeled as 100 proof and taxed as such. In Britain, where this “sophisticated” method of measuring alcoholic content originated, the proof point was determined to be 57% alcohol by volume.

Even today, the higher the percentage of alcohol in the bottle, the higher the taxes are on that bottle and the more expensive it is to purchase. To be labeled a spirit, the bottle must contain a minimum percentage of 40% alcohol, which is also the least expensive.

Life is simple in the U.S., especially when calculating alcohol percentage and proof: Just multiply by 2. So, a 40% ABV spirit is 80 proof. But if there is only 40% alcohol in the bottle, what else are you drinking? Water. And that’s one of the elements that give each bottle of scotch, bourbon or any other spirit its distinguishing taste.

Liquor isn’t the only alcoholic beverage requiring an ABV designation, but it IS the only one that must designate proof. Wine and beer manufacturers label each bottle with its ABV. Wines range from 10% to 14% ABV, while beer runs in the 5% range. To find its proof, you can do a simple calculation by doubling the ABV of your bottle of wine.

The bottles of whiskey, rum, gin or unflavored vodka staring at you from the sales display in your favorite liquor emporium are usually labeled “100%,” which means they’re 50% alcohol. The fancy flavored vodkas have less alcohol and more flavoring, giving them a proof reading around 70, or 35% alcohol.

Your chocolate vodka martini may put you under the table sooner than a gin and tonic, even if the gin has more alcohol than the vodka. Diluting the alcohol with a mixer means a smaller amount of concentrated alcohol is running through your bloodstream. Ice, the size of the shot, the glass size and the amount of mixer ‒ all affect the proof of your cocktail.

When in France... if you’re drinking liquor, forget calculations. What you read on the label is what you get. One hundred proof equals 100% alcohol. Keep that in mind when shopping at the duty-free on your way out of France!

A glass of scotch, a gin and tonic with lemon, or even a glass of dry white wine are all comforting drinks after a trying day. They’re your reward, and most likely, well-earned. Pace yourself. If you find yourself ordering or pouring a second drink, make sure to drink a glass of water between drinks. Just as scotch is diluted with water at the distillery, you can further dilute the alcohol running through your body with water. Drink sensibly.