ABV vs Proof: How to Read a Spirits Label
Every spirits label states the alcohol content. In most of the world this is shown as "ABV" — Alcohol By Volume, expressed as a percentage. In the US, both ABV and "proof" are commonly shown. The two scales are simply related — but understanding what the numbers mean reveals a lot about how a spirit is made.
ABV
ABV — Alcohol By Volume — is the volumetric percentage of ethanol in the bottle. A 40% ABV spirit is 40% pure ethanol and 60% water (plus a tiny amount of flavour compounds). 40% ABV is the global legal minimum for most spirits categories — Scotch whisky must be bottled at 40% or higher; bourbon similarly; gin minimum 37.5% in the EU, 40% in the US.
Proof
"Proof" is the older American measure: ABV × 2. So 40% ABV = 80 proof; 50% = 100 proof. The term originates from a 17th-century test: spirit was poured onto gunpowder and lit. If the gunpowder burned, the spirit was sufficiently strong (the water content low enough). The minimum strength at which this would happen was defined as "100 proof" in the UK (which corresponds to 57.15% ABV). The US later simplified the scale to "200 proof = pure alcohol," making the US proof exactly twice the ABV.
UK proof (historical)
UK proof — used until 1980 — was a different scale: 100 UK proof = 57.15% ABV. The US system uses 100 proof = 50% ABV. "Imperial Pint of 100 proof rum" historically meant 57.15% ABV — much stronger than the modern American 100 proof. The UK abandoned the proof system officially in 1980, but the term "Navy Strength" (around 57% ABV) preserves the historical meaning.
What a high ABV actually means
A 40% ABV bottle has been diluted from cask strength (typically 60-65% at filling, drifting downward in cool climates over decades). At bottling, water is added to bring the spirit down to the target strength. The trade-off: 40% is easier to drink, more accessible; higher strength preserves more flavour intensity (and more cask character).
Cask strength
"Cask strength" or "barrel proof" means the spirit is bottled at the natural strength it came out of the cask — no water added. Cask-strength expressions range typically from 50-65% ABV. Stagg Jr. (Buffalo Trace) often comes out around 65%; Aberlour A'Bunadh around 60%; Booker's Bourbon 60-65%; Macallan Cask Strength around 58%. The drinker can add water to taste; the bottle has the maximum flavour density.
Bottled in Bond
A specifically American category: "Bottled in Bond" whiskey must be exactly 100 proof (50% ABV), aged at least 4 years, the product of one distillation season at one distillery, bottled under government supervision. The Bottled-in-Bond Act of 1897 was one of the first US consumer protection laws.
Navy strength
"Navy strength" — historically 57.15% ABV in the UK system — is used for gins (Plymouth Navy Strength, Hayman's Royal Dock, Sipsmith V.J.O.P.) and some rums. The historical context: British Royal Navy rum, stored alongside gunpowder, had to be strong enough that, if spilt on the powder, it would not prevent the powder from burning.
Reading the label
A bourbon bottle says "100 proof" — that's 50% ABV. A Scotch bottle says "43% vol." — that's 86 US proof. A "cask strength" or "barrel proof" bottle is undiluted from the cask. A "Bottled in Bond" bottle is exactly 50% ABV. Now you know what those numbers mean.
Plan your next trip
The legal minimum ABV varies by category and country. The interactive map shows where each category is produced; the bottle labels reveal everything else.