In the United States, proof is twice the alcohol by volume. An 80 proof spirit is 40 percent alcohol, 100 proof is 50 percent, and 200 proof would be pure ethanol. The definition is written into federal regulation, and 80 is the number you see most often because it is the lowest strength the law allows for vodka, gin, whiskey, rum, brandy and tequila. Here is the legal definition, why 80 is the floor, what proof means for a standard drink and for calories, how proof is different in Britain, and where the word came from.
Last verified September 13, 2026. Definitions and minimums are quoted from 27 CFR part 5 (sections 5.1, 5.65, 5.88 and 5.142 through 5.151), standard drinks from NIAAA, calories from USDA FoodData Central, history from Difford’s Guide and the sources listed at the end.
| 80 proof | Fact |
|---|---|
| Alcohol by volume | 40% |
| Legal definition | 27 CFR 5.1: proof is “twice the percentage of ethyl alcohol by volume” at 60 F |
| Why it matters | Minimum bottling strength for whisky, gin, vodka, rum, brandy and agave spirits (27 CFR 5.142 to 5.148) |
| Standard drinks in a 1.5 oz shot | Exactly 1.0 (0.6 fl oz of pure alcohol, the NIAAA definition) |
| Standard drinks in a 750 mL bottle | 16.9 |
| Calories in a 1.5 oz shot (USDA) | 96 to 97 |
| What has to be on the label | Percent alcohol by volume; proof is optional (27 CFR 5.65) |
| Same as 80 proof in Britain? | No. On the old UK scale, 80 proof was 45.7% ABV; the UK dropped proof in 1980 |
The legal definition
Title 27 of the Code of Federal Regulations, section 5.1, defines proof as “the ethyl alcohol content of a liquid at 60 degrees Fahrenheit, stated as twice the percentage of ethyl alcohol by volume.” That is the whole rule. Divide the proof by two and you have the ABV; multiply the ABV by two and you have the proof. The temperature matters because alcohol and water both expand when warm, so the percentage is fixed at a reference temperature.
Proof is not actually required on a US label. Under 27 CFR 5.65 the alcohol content “must be stated on the label as a percentage of alcohol by volume,” in a form such as “40% alc/vol,” and the proof “may be stated on a label as long as it appears in the same field of vision as the mandatory statement.” The regulation also allows a tolerance of plus or minus 0.3 percentage points between the labeled and actual ABV. So the “80 proof” on a bottle is a courtesy; the “40% alc/vol” next to it is the legal statement.
Why 80 is the floor
The federal standards of identity in 27 CFR part 5, subpart I, set a minimum bottling strength for each class of spirit, and for the major classes it is the same number.
| Section | Class | Minimum bottling strength | Other rules in the standard |
|---|---|---|---|
| 5.142 | Neutral spirits and vodka | 40% ABV (80 proof) | Must be distilled at or above 95% (190 proof); vodka may carry up to 2 g/L sugar and 1 g/L citric acid |
| 5.143 | Whisky | 40% ABV (80 proof) | Types such as bourbon and rye have their own distillation and barrel rules |
| 5.144 | Gin | 40% ABV (80 proof) | |
| 5.145 | Brandy | 40% ABV (80 proof) | |
| 5.146 | Blended applejack | 40% ABV (80 proof) | |
| 5.147 | Rum | 40% ABV (80 proof) | |
| 5.148 | Agave spirits (tequila, mezcal) | 40% ABV (80 proof) | |
| 5.150 | Cordials and liqueurs | No minimum in the standard | Must contain at least 2.5% sugar by weight |
| 5.151 | Flavored spirits (flavored vodka, rum, whisky, gin, brandy) | 30% ABV (60 proof) |
That table explains most of what you see on a shelf. A bottle labeled “vodka” or “whiskey” cannot legally be weaker than 80 proof, which is why so many bottles sit at exactly 80. A flavored vodka can go down to 60 proof, and some do, which is why a bottle of flavored vodka and a bottle of plain vodka from the same brand often show different numbers. A liqueur has no floor at all, only a sugar minimum, so liqueur strengths vary widely and the label is the only guide.
There is a tax reason to bottle at the floor, too. Federal excise tax on spirits is charged per proof gallon, a gallon of liquid at 50 percent alcohol (27 CFR 5.1), at $13.50 at the general rate. The tax follows the alcohol, not the bottle, so a 100 proof bottling carries 25 percent more federal tax than the same bottle at 80 proof: about $2.14 on a 750 mL bottle at 80 proof and $2.67 at 100 proof.
What 80 proof means for a drink
NIAAA defines a US standard drink as 0.6 fluid ounces (14 grams) of pure alcohol and gives the spirits example as a 1.5 oz shot at about 40 percent alcohol. The math is exact: 1.5 x 0.40 = 0.60. That is why every standard-drink chart and most cocktail recipes assume 80 proof. Change the proof and the same pour is a different number of drinks.
| Proof | ABV | Pure alcohol in a 1.5 oz shot | Standard drinks per shot | Standard drinks per 750 mL bottle |
|---|---|---|---|---|
| 80 | 40% | 0.60 oz | 1.00 | 16.9 |
| 86 | 43% | 0.65 oz | 1.08 | 18.2 |
| 90 | 45% | 0.68 oz | 1.13 | 19.0 |
| 100 | 50% | 0.75 oz | 1.25 | 21.1 |
| 120 | 60% | 0.90 oz | 1.50 | 25.4 |
| 151 | 75.5% | 1.13 oz | 1.89 | 31.9 |
| 190 | 95% | 1.43 oz | 2.38 | 40.2 |
The formula for any pour: standard drinks = (fluid ounces x ABV) / 0.6. A 2 oz pour of a 100 proof bourbon is 2 x 0.5 / 0.6 = 1.67 standard drinks. Swap a 100 proof spirit into a recipe written for 80 proof and the drink carries 25 percent more alcohol at the same pour, which is why bartenders adjust the dilution or the mixer when they make the switch.
Calories by proof
Unflavored spirits carry no sugar, fat or protein worth counting, so their calories come from the alcohol alone and rise with proof. USDA FoodData Central lists distilled spirits (gin, rum, vodka, whiskey) at several proofs, per 1.5 oz jigger:
| Proof | Calories per 1.5 oz | Grams of alcohol per 1.5 oz | USDA FDC ID |
|---|---|---|---|
| 80 | 96 | 14.0 | 174815 |
| 86 | 105 | 15.1 | 171919 |
| 90 | 110 | 15.9 | 171920 |
| 94 | 116 | 16.7 | 173663 |
| 100 | 124 | 17.8 | 173664 |
USDA’s separate entry for 80 proof vodka (FDC 174818) rounds to 97 per jigger; the one-calorie difference is rounding on the portion weight. Flavored spirits and liqueurs contain sugar and are not covered by these figures. The full breakdown across spirits, beer and wine is in How Many Calories Are in a Shot of Rum.
Common bottlings and their proofs
Producer sites and state-store listings, checked at verification. This is a reference for reading labels, not a ranking.
| Proof | ABV | Example |
|---|---|---|
| 80 | 40% | Jack Daniel’s Old No. 7 Tennessee Whiskey |
| 86 | 43% | Old Forester 86 Proof Kentucky Straight Bourbon |
| 90 | 45% | Maker’s Mark Kentucky Straight Bourbon Whisky |
| 100 | 50% | Evan Williams Bottled-in-Bond Bourbon |
| 101 | 50.5% | Wild Turkey 101 Kentucky Straight Bourbon |
| 120 | 60% | Everclear 120 proof (sold mainly in California) |
| 151 | 75.5% | Everclear 151 proof (Bacardi 151 was discontinued in 2016) |
| 190 | 95% | Everclear 190 proof |
Bottled in bond: the 100 proof rule
One proof figure has its own law. The Bottled-in-Bond Act, signed March 3, 1897, created a federal guarantee for straight whiskey and is often called the first US consumer-protection law. Its modern form is 27 CFR 5.88, and the requirements are strict: the spirits must be the product of one distiller at one distillery in one distilling season, aged at least four years in wood, unaltered except by filtration and similar physical treatments, “reduced in proof by the addition of only pure water to 50 percent alcohol by volume (100 degrees of proof),” and bottled at exactly 100 proof. The label must show the distillery and bottling plant numbers. So when a label says “bottled in bond,” 100 proof is not a choice; it is the definition.
Where the word “proof” comes from
The word comes from Britain, where spirit strength was tested, or “proved,” for excise and naval purposes from the 1600s on. The well-known story is that sailors soaked gunpowder in rum and checked whether it still lit; if it did, the spirit was “proof.” Difford’s Guide, which has looked for the evidence, calls it a legend and says it can point to no written record of the test. What is documented is the instrument that replaced any such test: Bartholomew Sikes’s hydrometer, developed around 1816 and adopted into British law shortly after. On the Sikes scale, 100 proof was a spirit with twelve thirteenths the specific gravity of water, which works out to 57.15 percent alcohol by volume, and UK proof degrees were 1.75 times the ABV.
The United States went a different way around 1848 and defined proof on the percentage of alcohol rather than on specific gravity: 50 percent alcohol by volume became 100 proof, which is the rule still in 27 CFR 5.1 today. The two scales caused confusion for more than a century. A bottle at “80 proof” in London was 45.7 percent alcohol; the same words in New York meant 40 percent. Britain gave up proof for ABV on January 1, 1980, and the EU labels ABV only, so proof is now essentially an American labeling convention.
One more thing the British history explains: “navy strength” gin and rum at 57 percent are named for the old 100 UK proof, though Difford’s notes the Royal Navy’s rum ration was actually issued at 54.5 percent, so the 57 percent figure comes from the old proof scale rather than from a naval standard.
Frequently asked questions
What does 80 proof mean? 40 percent alcohol by volume. In the US, proof is always twice the ABV.
Is 80 proof strong? It is the legal minimum for vodka, gin, whiskey, rum, brandy and tequila in the US, and the strength that defines a standard drink: a 1.5 oz shot at 80 proof is one standard drink.
What is 100 proof? 50 percent alcohol by volume. A 1.5 oz shot is 1.25 standard drinks. Bottled-in-bond spirits are 100 proof by law.
What is the highest proof you can buy? Everclear 190 is 95 percent; Spirytus Rektyfikowany is 96 percent (192 proof). Several states restrict spirits above 151 or 153 proof; see What Is Everclear?
Is 80 proof the same as 40 percent? Yes, in the US. On the old British scale, 80 proof was 45.7 percent, but the UK stopped using proof in 1980.
Does proof change the calories? Yes. Calories in an unflavored spirit come from the alcohol, so a 100 proof shot has about 124 calories against 96 for an 80 proof shot (USDA).
Sources
- 27 CFR 5.1, Definitions: proof and proof gallon (eCFR), checked September 13, 2026
- 27 CFR 5.65, Alcohol content (eCFR), checked September 13, 2026
- 27 CFR 5.88, Bottled in bond (eCFR), checked September 13, 2026
- 27 CFR part 5, subpart I, Standards of identity for distilled spirits (eCFR), checked September 13, 2026
- TTB tax and fee rates, checked September 13, 2026
- NIAAA Rethinking Drinking, What is a standard drink, checked September 13, 2026
- USDA FoodData Central, distilled spirits 80 proof (FDC 174815), with entries 171919 (86 proof), 171920 (90 proof), 173663 (94 proof) and 173664 (100 proof), checked September 13, 2026
- Difford’s Guide, Overproof and navy strength and Alcohol content explained: ABV, proof, units, checked September 13, 2026
- Wikipedia, Alcohol proof (citing W. B. Jensen, “The Origin of Alcohol ‘Proof’,” Journal of Chemical Education, 2004, and the Scotch Whisky Association), used for the 1816, 1848 and 1980 dates, checked September 13, 2026
- Michael Veach, 128 years of bottled-in-bond whiskey (March 3, 2025), checked September 13, 2026
- Producer pages for the proof examples: Jack Daniel’s Old No. 7; Old Forester 86 Proof; Maker’s Mark; Evan Williams Bottled-in-Bond; Wild Turkey 101; Luxco product specifications (Everclear); Bacardi, The legend of Bacardi 151, checked September 13, 2026
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