US proof is exactly twice the alcohol by volume, defined that way in 27 CFR 30.11. Divide by two to read ABV from proof, multiply by two to go the other way. There is nothing hidden in it, which is why this page is a table rather than a calculator.
UK proof is the older Sikes scale and is not a doubling. 100 UK proof is about 57.15% ABV, the strength at which gunpowder soaked in spirit would still ignite. Multiply ABV by roughly 1.75 for a Sikes figure.
ABV to proof
| ABV | US proof | UK proof (Sikes) |
|---|---|---|
| 20% | 40 | 35.0 |
| 25% | 50 | 43.7 |
| 30% | 60 | 52.5 |
| 35% | 70 | 61.2 |
| 37.5% | 75 | 65.6 |
| 40% | 80 | 70.0 |
| 43% | 86 | 75.2 |
| 45% | 90 | 78.7 |
| 46% | 92 | 80.5 |
| 47% | 94 | 82.2 |
| 50% | 100 | 87.5 |
| 55% | 110 | 96.2 |
| 57.5% | 115 | 100.6 |
| 60% | 120 | 105.0 |
| 63% | 126 | 110.2 |
| 65% | 130 | 113.7 |
| 70% | 140 | 122.5 |
| 75% | 150 | 131.2 |
| 80% | 160 | 140.0 |
| 90% | 180 | 157.5 |
| 95% | 190 | 166.2 |
Proof to ABV
| US proof | ABV | UK proof (Sikes) |
|---|---|---|
| 40 | 20% | 35.0 |
| 50 | 25% | 43.7 |
| 60 | 30% | 52.5 |
| 70 | 35% | 61.2 |
| 80 | 40% | 70.0 |
| 86 | 43% | 75.2 |
| 90 | 45% | 78.7 |
| 94 | 47% | 82.2 |
| 100 | 50% | 87.5 |
| 110 | 55% | 96.2 |
| 114 | 57% | 99.7 |
| 120 | 60% | 105.0 |
| 127 | 63.5% | 111.1 |
| 130 | 65% | 113.7 |
| 138 | 69% | 120.7 |
| 140 | 70% | 122.5 |
| 150 | 75% | 131.2 |
| 151 | 75.5% | 132.1 |
| 160 | 80% | 140.0 |
| 180 | 90% | 157.5 |
| 190 | 95% | 166.2 |
| 200 | 100% | 175.0 |
The strengths that show up on labels, and why
80 proof, 40% ABV. The legal minimum for most spirits in both the EU and the US. If a bottle does not say otherwise, this is what it is.
86 proof, 43% ABV. A common export strength. High enough to carry aroma, low enough to stay under duty thresholds that step at higher strengths in some markets.
92 proof, 46% ABV. The usual floor for non-chill-filtered whisky. Below roughly this strength, fatty acid esters come out of solution when the spirit is chilled or watered, and the bottle goes cloudy. Filtering removes them and some flavour with them, so bottling at 46% avoids the choice.
100 proof, 50% ABV. Bottled-in-Bond in the US requires exactly this, plus one distilling season, one distiller, and four years in a federally bonded warehouse. The proof is the least of it.
114 proof, 57.15% ABV. Navy strength. The gunpowder test: spirit at this strength or above, spilled on powder, still lights. Below it, the powder is too wet to catch.
151 proof, 75.5% ABV. Sold mostly for flaming drinks and infusions. Flammable enough that several countries restrict it.
Reading proof off a hydrometer
A proof hydrometer is calibrated at a single temperature, 60 °F in the US and 20 °C almost everywhere else. Warm spirit is less dense, so the instrument floats lower and reads high. A sample at 30 °C reading 84% is really closer to 80.5%.
That error is larger than most people expect and it moves with strength, not just temperature. Correct the reading before you convert it to proof, otherwise you are converting the wrong number precisely. The temperature correction calculator handles it, or the proof converter if you already have a corrected figure.