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Proof to ABV converter
In the United States, proof is exactly double ABV. Type either number and the other appears.
Type in either box. US proof is exactly twice ABV. Historical British proof used a different scale; 100 British proof was about 57.1% ABV.
The conversion
80 proof is 40 percent. 100 proof is 50 percent. 125 proof is 62.5 percent. Where proof came from, and why British proof was different.
Why blenders care
Scotch, Irish, and Japanese whiskies label ABV; American whiskey labels proof. Blending across them means converting everything to one unit first. The most common home blending arithmetic error is treating a 45 (ABV) and a 90 (proof) as different strengths. They are identical.
The app that keeps these books for you
Thief & Blend tracks every pour, runs the proof math live, and remembers how much of the first pour survives. On the App Store for iPhone.
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