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
This calculator provides estimates for informational purposes only. It is not a substitute for professional consultation with a licensed sommelier, beverage consultant, or regulatory authority. ABV conversions are mathematically exact for ABV ↔ Proof. Specific gravity estimates use the standard homebrew formula and become 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.
How This Calculator Works
When converting from ABV, US Proof is simply ABV × 2 and UK Sikes Proof is ABV × 1.75. Gay-Lussac degrees are numerically equal to ABV. When converting from specific gravity readings, the calculator uses the standard homebrew formula: ABV = (OG − FG) × 131.25, where OG is the Original Gravity before fermentation and FG is the Final Gravity after fermentation. This formula derives from the density change caused by converting sugar to ethanol and CO₂. The estimated OG and FG shown in reverse calculations assume 75% apparent attenuation, a typical value for ale yeast strains.
References & Methodology
- Alcohol and Tobacco Tax and Trade Bureau (TTB), 27 CFR §5.37 — Legal definition of proof for distilled spirits in the United States: "Proof is the ethyl alcohol content of a liquid at 60° Fahrenheit stated as twice the percent of ethyl alcohol by volume."
- Wine & Spirit Education Trust (WSET) (2023) — WSET Level 3 Award in Wines Study Guide. Standard reference for ABV measurement, labeling conventions, and beverage classification worldwide.
- Balling, C. J. N. (1843) — Original gravity-to-alcohol relationship. The simplified modern form (OG − FG) × 131.25 is derived from Balling's plato-based tables and is widely cited in brewing science literature.
- HM Revenue & Customs (HMRC) — Historical Sikes hydrometer system documentation. The UK Sikes proof scale, used from 1816 to 1980, defined 100° proof as approximately 57.15% ABV.