Proof to ABV Converter
Updated
Convert Proof to ABV (and Back)
Enter a value into any field below — US Proof, UK Proof, or ABV% — and the other two update instantly. US Proof is always exactly twice the ABV% (80 proof = 40% ABV). UK Proof is the older imperial scale, replaced by ABV in UK law in 1980, where 100 degrees proof equals approximately 57.15% ABV.
Strength
Alcohol by weight (ABW)
Distilling and need to dilute a high-proof spirit down to a target strength? Use the Alcohol Dilution Calculator to work out exactly how much water to add.
How to Use This Proof Converter
- Know your starting value. Check the bottle label or your alcoholmeter/hydrometer reading — is it in ABV%, US proof, or UK (Sikes) proof?
- Type it into the matching field. There’s no need to select a mode first — just enter the number into whichever field matches what you have.
- Read off the other two values. They update immediately, along with an approximate alcohol-by-weight (ABW) figure and a visual strength meter.
If you’re taking a hydrometer or alcoholmeter reading yourself rather than converting a label figure, remember that alcohol readings are temperature-sensitive. Use the Hydrometer Temperature Correction tool first if your sample wasn’t at the calibration temperature (typically 60°F / 15.6°C or 20°C, depending on your instrument).
US Proof vs. UK Proof vs. ABV — What’s the Difference?
Alcohol by Volume (ABV)
ABV is the international standard — the percentage of a beverage’s total volume that is pure ethanol. It’s defined as millilitres of ethanol per 100 mL of solution at a reference temperature (usually 20°C), and it’s the figure required on nearly all commercial alcohol labelling worldwide today.
US Proof
Since 1848, the US definition of proof has been simple: proof is exactly twice the ABV percentage. A spirit at 40% ABV is 80 proof; a cask-strength whiskey at 65% ABV is 130 proof. This is the version most people mean when they say “proof” today.
UK Proof (Historical “Sikes” Scale)
The UK used a different system until 1980, based on the specific gravity of the spirit relative to water rather than a clean multiple of ABV. Under this “Sikes” scale, 100 degrees proof corresponds to approximately 57.15% ABV — the concentration at which the spirit’s density was historically defined as exactly 12/13 that of water at 51°F. The UK legally replaced this system with ABV under the Weights and Measures Act 1979 (in force from 1980), so you’ll mostly encounter UK proof today in older recipes, historical documents, or antique spirits.
Alcohol by Weight (ABW)
Some US state regulations and older nutrition labels express strength as ABW instead of ABV. Because ethanol is less dense than water, ABW is always a lower number than ABV for the same spirit — roughly ABW ≈ ABV × 0.789 (ethanol’s density in g/mL). This converter shows an approximate ABW figure alongside your ABV result.
Proof to ABV — Quick Reference Chart
| US Proof | ABV % | UK Proof (≈) | Typical example |
|---|---|---|---|
| 40 | 20% | 35 | Liqueurs, cordials |
| 60 | 30% | 52.5 | Lower-strength spirits |
| 70 | 35% | 61.3 | Some flavoured spirits |
| 80 | 40% | 70 | Standard vodka, gin, whiskey |
| 90 | 45% | 78.8 | Higher-strength bottlings |
| 92 | 46% | 80.5 | Common non-chill-filtered whisky strength |
| 100 | 50% | 87.5 | Overproof-adjacent spirits |
| 110 | 55% | 96.3 | Cask-strength whisky (lower end) |
| 130 | 65% | 113.8 | Cask-strength whisky (upper end) |
| 151 | 75.5% | 132.1 | Overproof rum |
| 190 | 95% | 166.3 | Neutral grain spirit |
| 200 | 100% | 175 | Pure ethanol (theoretical) |
Where Proof Conversion Matters
Bottling Strength Standards
Most spirits-labelling regulations set 40% ABV (80 US proof) as the standard minimum strength for a product to be legally sold as a “spirit” in most major markets, including under US TTB rules. Some distillers bottle at 46% ABV (92 proof) instead, since spirits above roughly this strength don’t require chill filtration to stay clear at refrigerator temperatures.
Cask Strength / Barrel Proof
“Cask strength” or “barrel proof” spirits are bottled without dilution, typically landing between 55–65% ABV (110–130 proof) depending on how long the spirit aged and how much water evaporated from the barrel (the “angel’s share”).
During a Distillation Run
If you’re running a pot still, the proof of the distillate falls steadily throughout the run — hearts typically come off in the 60–75% ABV range before tailing off toward the end. If your alcoholmeter or proof hydrometer reads in proof rather than ABV, this converter lets you cross-check readings against your target cut points without doing the arithmetic by hand mid-run. For calculating the alcohol content of a fermented wash before distillation, see the main ABV Calculator, which works from original and final gravity readings.
Mixing spirits into cocktails and want the final drink’s ABV? Try the Cocktail ABV Calculator — enter each ingredient’s volume and ABV for an exact blended result.
Frequently Asked Questions About Proof and ABV
What is 80 proof in ABV?
80 proof is 40% ABV. On the US scale, proof is always exactly double the ABV percentage, so dividing 80 by 2 gives 40% alcohol by volume — the standard strength for most vodka, gin, and whiskey.
Is 100 proof strong?
Yes — 100 proof (50% ABV) is well above standard bottling strength. Most common spirits like vodka and whiskey sit around 80 proof (40% ABV); 100 proof is considered a stronger-than-average bottling, though still short of cask-strength territory (110–130 proof).
How do I convert proof to a percentage?
Divide US proof by 2 to get the ABV percentage. For example, 150 proof ÷ 2 = 75% ABV. If you’re working with the older UK proof scale instead, multiply the UK proof value by 4⁄7 (approximately 0.5714) rather than dividing by 2.
What’s the difference between US proof and UK proof?
US proof is exactly 2 × ABV%; UK proof is not. The historical UK “Sikes” scale defined 100 degrees proof as approximately 57.15% ABV, based on the spirit’s density relative to water rather than a clean multiple. The UK legally switched to labelling spirits in ABV in 1980, so UK proof is now mostly seen only in historical or vintage contexts.
Why did the UK stop using proof?
The UK adopted ABV as its legal strength measure under the Weights and Measures Act 1979 (effective 1980), aligning with the international ABV standard used across most of Europe and making labels directly comparable across countries without needing a conversion.
What is the difference between ABV and ABW?
ABV measures alcohol as a share of volume; ABW measures it as a share of weight. Because ethanol is lighter than water, ABW is always a lower number than ABV for the same drink — roughly ABW ≈ ABV × 0.789. Some older US labelling regulations use ABW instead of ABV.
What proof is pure alcohol?
Pure ethanol is 200 US proof, or 100% ABV. In practice, commercially available “pure” grain alcohol tops out around 190–195 proof (95–97.5% ABV), since ethanol and water form an azeotrope that ordinary distillation can’t fully separate past roughly 95.6% ABV.
Why do some spirits list both proof and ABV on the label?
Some markets and brands show both figures for clarity, since “proof” remains a familiar marketing term in the US (particularly for whiskey and rum) even though ABV is the figure used for tax and regulatory purposes. Showing both avoids confusion for drinkers used to either system.
How accurate is a proof hydrometer or alcoholmeter reading?
Proof and ABV readings are both temperature-sensitive, and most instruments are calibrated to a specific reference temperature (commonly 60°F/15.6°C or 20°C). A reading taken well above or below that temperature needs correcting before you convert it — see the Hydrometer Temperature Correction tool for the adjustment.