ABV ↔ Proof Converter
Convert between alcohol by volume, US proof and UK (Sikes) proof.
Overview
The ABV to Proof Converter translates between the three units used to describe the alcohol content of a beverage: alcohol by volume percentage, United States proof and the older United Kingdom (Sikes) proof. Whether you're reading a vintage bottle, working through an import label or comparing a recipe written for a different market, this converter saves the mental arithmetic.
Bartenders, distillers, sommeliers and home brewers all run into proof on labels and tasting notes, but the underlying definition shifts by country. The tool gives you a single place to look up alcohol by volume to US proof, Sikes proof to ABV and degrees proof Imperial vs metric — three of the most searched conversions in spirit labelling.
How it works
US proof is defined as exactly twice the alcohol by volume, so a 40 percent ABV whiskey is 80 proof, and 50 percent ABV vodka is 100 proof. The relationship is linear in both directions: ABV equals proof divided by two, and proof equals ABV multiplied by two.
UK Sikes proof is a legacy hydrometer scale where "100 proof" originally meant 57.15 percent ABV — the strength at which gunpowder soaked in spirit would still ignite. To convert, multiply ABV by roughly 1.7505, and divide a Sikes proof figure by 1.7505 to recover ABV. The converter handles all three pairings and clamps results to the 0 to 100 percent ABV range.
Examples
40% ABV → 80 US proof → 70 UK (Sikes) proof
57.15% ABV → 114.3 US proof → 100 UK (Sikes) proof
100 US proof → 50% ABV → 87.5 UK (Sikes) proof
70 UK (Sikes) proof → 40% ABV → 80 US proof
FAQ
Why is UK proof different from US proof?
The UK scale predates modern hydrometers and is anchored to the gunpowder ignition test. The US adopted a simpler doubling convention in 1848 because it is easier to print on labels.
Is UK proof still in use?
Britain officially moved to alcohol by volume in 1980, so the Sikes scale is mostly historical. You may still see it on antique bottles, naval rum labels and some Commonwealth exports.
Does proof mean the same thing for beer and wine?
Proof is almost never used for beer or wine. Both are labelled in ABV worldwide, so the converter is mainly useful for distilled spirits.
Can ABV go above 100?
No. By definition ABV is the volume fraction of ethanol, capped at 100 percent. US proof can reach 200 in theory but real bottlings rarely exceed 190 because absolute ethanol absorbs moisture from the air.
How accurate is the Sikes conversion?
The 1.7505 factor matches the legal definition. Practical accuracy is limited by temperature, since spirit volume changes about 0.04 percent per degree Celsius.