ABV Calculator — Alcohol by Volume, Proof & Specific Gravity Converter
Alcohol by Volume (ABV) is the standard measure of alcohol content used worldwide. In the United States, proof is defined as exactly twice the ABV percentage. Specific gravity — the ratio of a liquid's density to water — is used by brewers and distillers during fermentation to estimate alcohol content from hydrometer readings. This calculator converts between all three measurements instantly.
Convert ABV / Proof / Specific Gravity
ABV conversions are mathematically exact for ABV ↔ Proof. Specific gravity estimates use the standard homebrew formula (ABV = (OG − FG) × 131.25) which is accurate for most fermented beverages but becomes less precise above 12% ABV. Professional distillers should use TTB tables for regulatory compliance.
Understanding ABV, Proof, and Specific Gravity
ABV (Alcohol by Volume)
ABV expresses alcohol content as a percentage of total volume at 20°C (68°F). A wine at 13.5% ABV contains 13.5 mL of pure ethanol per 100 mL of liquid. ABV is the international standard used on all beverage labels in the EU, US, and most countries worldwide.
US Proof
The US proof system is straightforward: proof equals ABV multiplied by two. An 80-proof spirit is 40% ABV. This system was established by the US Tax and Trade Bureau (TTB) and replaced an older system based on gunpowder ignition tests.
Specific Gravity
Specific gravity measures density relative to water (SG = 1.000). Before fermentation, dissolved sugars raise the reading (Original Gravity, typically 1.040–1.090 for beer). After fermentation, the reading drops (Final Gravity, typically 1.005–1.015). The difference estimates alcohol produced.
| Beverage | Typical ABV | US Proof |
|---|---|---|
| Light Beer | 3.5–4.5% | 7–9 |
| Standard Beer / Ale | 4.5–6.5% | 9–13 |
| White Wine | 11–14% | 22–28 |
| Red Wine | 12–15% | 24–30 |
| Fortified Wine (Port, Sherry) | 17–22% | 34–44 |
| Liqueurs | 15–30% | 30–60 |
| Standard Spirits | 40% | 80 |
| Cask Strength Whisky | 50–65% | 100–130 |
| Overproof Rum | 57–75% | 114–151 |
| Neutral Grain Spirit | 95% | 190 |
Frequently Asked Questions
Why is US proof exactly double ABV?
The modern US proof system was standardized in 1848 and formalized by federal regulation. The doubling convention was chosen for simplicity after the earlier “gunpowder test” (where spirit was deemed “proof” if it could ignite gunpowder) fell out of use. The UK used a different system (Sikes) based on specific gravity until 1980, when it adopted ABV.
How accurate is the OG/FG method?
The standard homebrew formula (OG − FG) × 131.25 is reliable for beers and wines below 12% ABV. For higher-gravity fermentations, more complex formulas (such as Balling or the extended formula) are preferred. Professional lab analysis by distillation or density meter provides the most accurate results for regulatory labeling.