Proof is a number that tells you how much alcohol is in a spirit. In the United States, proof is simply double the alcohol by volume (ABV) percentage. An 80-proof bottle of vodka contains 40% alcohol, a 100-proof bourbon contains 50%, and so on. To convert in either direction, you either multiply ABV by two or divide proof by two.
How the US Proof System Works
The US proof system, established around 1848, is straightforward math. Fifty percent alcohol by volume was defined as 100 proof, making the formula a clean 2:1 ratio. A bottle labeled 90 proof contains 45% ABV. A bottle labeled 70 proof contains 35% ABV. Every two proof points equal one percentage point of alcohol.
This system applies only to distilled spirits. Beer and wine labels in the US display alcohol content as ABV, not proof. You won’t see a bottle of wine labeled “28 proof” even though it technically could be. Federal regulations require spirits to list ABV, while proof can optionally appear alongside it. Most spirit producers include both on the label.
Common spirits like gin, rum, vodka, tequila, whiskey, and brandy are typically bottled at 80 proof (40% ABV). That’s the standard baseline for most of these categories. Some whiskeys and rums are bottled at higher strengths, often 90 to 114 proof, and “cask strength” or “barrel proof” releases can reach 120 to 140 proof. Liqueurs and flavored spirits tend to sit lower, sometimes in the 40 to 70 proof range.
Why 200 Proof Is the Maximum
Since proof is double the ABV, 200 proof would be pure ethanol at 100% alcohol. In practice, standard distillation can only get you to about 95.6% ABV (roughly 191 proof). This ceiling exists because ethanol and water form what chemists call an azeotrope: at that concentration, the two liquids evaporate at the same rate, so no amount of further distillation can separate them. The water molecules work their way into the ethanol’s surface layer at high concentrations, making it physically impossible to boil one off without the other.
Getting to true 200 proof requires special chemical techniques beyond normal distillation. Spirits you’ll find on a shelf top out well below this limit, typically between 80 and 151 proof.
The UK Used a Completely Different Scale
The word “proof” originated in 16th-century England, where spirits were taxed based on alcohol content. The original test was literal: if you could soak gunpowder in a spirit and still ignite it, the spirit was “above proof.” If it wouldn’t burn, it was “under proof.” A spirit just strong enough to sustain combustion was called 100 proof.
In 1816, England replaced this fire test with a measurement based on specific gravity, defining 100 proof as a spirit with a density of 12/13 that of pure water. This worked out to about 57.15% ABV, meaning British 100 proof was significantly stronger than American 100 proof (50% ABV). To convert old British proof to ABV, you’d multiply by 4/7 rather than simply dividing by two. Under that scale, pure alcohol was 175 proof, not 200.
Britain abandoned its proof system on January 1, 1980, switching to the ABV standard used across Europe. Today, the US is essentially the only major market that still uses proof on labels. If you’re reading a bottle from anywhere outside the United States, the number you see is almost certainly ABV, not proof.
Quick Conversions for Common Spirits
- 80 proof = 40% ABV (standard vodka, gin, rum, tequila, whiskey)
- 86 proof = 43% ABV (many single malt scotches)
- 90 proof = 45% ABV (some bourbons and rye whiskeys)
- 100 proof = 50% ABV (bonded whiskeys, some rums)
- 114 proof = 57% ABV (higher-strength bourbons)
- 151 proof = 75.5% ABV (overproof rums)
When comparing drinks of different proofs, the alcohol content difference matters more than it looks. A 1.5-ounce shot of 100-proof whiskey delivers 25% more alcohol than the same pour of 80-proof whiskey. The CDC defines one standard drink as 1.5 ounces of 80-proof (40% ABV) liquor, so higher-proof spirits pack more than one standard drink into the same glass.