ABV to Proof Converter: US Proof, UK Proof, °GL and Alcohol by Weight
Convert alcohol by volume to US proof (ABV × 2), old UK Sikes proof (ABV × 1.75), French Gay-Lussac degrees and alcohol by weight, or any of them back to ABV. Also shows pure alcohol per bottle, standard drinks per bottle and per serving for five countries, and US proof gallons.
How it works
US proof = 2 × ABV; UK (Sikes) proof = 1.75 × ABV (100° UK proof = 57.15% ABV); °GL = ABV; ABW from ABV with the ethanol–water density table (40% ABV ≈ 33.3% ABW); pure alcohol (g) = volume × ABV × 0.789 g/mL; standard drinks = grams ÷ 14 (US), 8 (UK), 10 (AU); proof gallons = US gallons × proof ÷ 100
“Proof” comes from an old test: gunpowder soaked in a spirit that would still ignite “proved” the spirit was strong, roughly 57% alcohol. Britain fixed that point as 100° proof with the Sikes hydrometer (a spirit weighing 12/13 of the same volume of water, 57.15% ABV), so old UK proof is about 1.75 times the ABV and spirits were described as so many degrees over proof (OP) or under proof (UP). The UK moved to ABV labels in 1980. In the United States proof is defined by TTB as twice the percent of alcohol by volume at 60 °F, so 80 proof is 40%. The French Gay-Lussac degree (°GL) is the same number as ABV. Alcohol by weight (ABW) is lower than ABV because ethanol is lighter than water, and because water and ethanol shrink by up to 4% when mixed. Older calculators use a single factor (0.789 ÷ 1) or ignore that contraction, which overstates ABW by about one point for spirits; this one interpolates the published ethanol–water table, so 40% ABV gives 33.3% ABW and 5% ABV gives 4.0% ABW. From ABV the calculator also works out grams of pure alcohol (density 0.789 g/mL), standard drinks per bottle and per serving for the US (14 g), UK (8 g), Australia and New Zealand (10 g), Canada (13.45 g) and Ireland (10 g), and US proof gallons, the unit federal excise tax on spirits is charged on.
Worked example
A 750 mL bottle of 40% ABV gin: US proof = 2 × 40 = 80; UK proof = 1.75 × 40 = 70°, which is 30° under proof; °GL = 40; alcohol by weight from the density table = 33.3%. Pure alcohol = 750 × 0.40 = 300 mL × 0.789 = 237 g, or 16.9 US standard drinks, 29.6 UK units and 23.7 Australian standard drinks. A 44 mL (1.5 fl oz) shot holds 14.0 g, almost exactly one US standard drink. The bottle is 750 ÷ 3,785.41 × 0.80 = 0.159 proof gallons.
Sources: TTB: 27 CFR Part 30, Gauging Manual (definition of proof and proof gallon) · Wikipedia: Alcohol proof (UK 57.15%, US 2 × ABV) · Wikipedia: Ethanol data page (ethanol–water % by volume vs % by mass) · NIAAA: What is a standard drink? (14 g)
Frequently asked questions
How do I convert ABV to proof?
In the US, double it: 40% ABV is 80 proof and 45% is 90 proof. Under the old UK system multiply by 1.75: 40% ABV is 70° proof.
Why is 100 UK proof 57.1%?
The Sikes definition made proof spirit the strength at which a spirit weighs 12/13 of an equal volume of water, which works out at 57.15% ABV. That is close to the lowest strength at which spirit-soaked gunpowder still burns.
Is “overproof” a fixed strength?
No. It means above 100 proof in the local system: over 50% ABV in the US, or over 57.1% under the old UK scale. A 151 rum is 75.5% ABV, 151 US proof and about 132° UK proof (32° OP).
What is the difference between ABV and ABW?
ABV is the share of the volume that is alcohol; ABW is the share of the weight. Because alcohol is lighter than water, ABW is always lower: about 4.0% ABW for a 5% beer and 33.3% ABW for a 40% spirit.
How many standard drinks are in a bottle of spirits?
A 750 mL bottle at 40% holds about 237 g of alcohol: about 17 US standard drinks of 14 g, or about 30 UK units of 8 g.
What is a proof gallon?
One US gallon of 100-proof spirit, or the same amount of alcohol in another volume and strength. A gallon at 80 proof is 0.8 proof gallons. US federal excise tax on distilled spirits is charged per proof gallon.
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Standard-drink figures are for information only and do not indicate a safe amount to drink or drive.