Proof Calculator
Enter an ABV or proof to convert it, or the volume and strengths of a spirit to get the water to add, the blend, or the proof gallons.
How to use the Proof Calculator
- In “What do you want to work out?”, choose one mode: “Convert ABV to proof, or proof to ABV”, “Dilute a spirit: water to add for a lower strength”, “Blend two spirits to a target strength” or “Proof gallons from a volume and strength”.
- Under “I enter strengths as”, pick “% ABV (alcohol by volume)” or “US proof”. This applies to every strength field.
- Fill in the fields for your mode:
- Convert: “Strength to convert” (0 to 100 for % ABV, 0 to 200 for proof).
- Dilute: “Spirit to dilute (starting volume)”, “Starting strength” and “Target strength”. The target must be above 0 and below the starting strength.
- Blend: “Total volume you want to make”, “Strength of spirit A”, “Strength of spirit B” (enter 0 for plain water) and “Target strength of the blend”. The target must lie between the two strengths.
- Proof gallons: “Volume of spirit” and “Strength of the spirit”.
- Read the results. Dilute mode shows “Water to add”, “Volume after dilution (ideal)” and “Pure alcohol in the batch”. Blend mode shows “Spirit A to use” and “Spirit B to use”. Proof gallons mode shows “Proof gallons” and “Wine gallons (US)”.
- Open “How it was calculated” to see each step with your own numbers.
To start quickly, use an example button such as “Cut 57 % to 40 %, 1 L”.
How do I convert ABV to proof?
Double the % ABV to get US proof. US proof is twice the percent alcohol by volume at 60 °F (about 15.6 °C), so 40 % ABV is 80 proof.
How do I convert proof to ABV?
Divide the proof by 2 to get % ABV. For example, 151 proof is 75.5 % ABV. Convert mode accepts 0 to 200 for proof, and any value outside that range shows an error naming the limit.
How much water do I add to dilute a spirit to 40 % ABV?
Use the ethanol balance. Final volume equals the starting volume times the starting strength, divided by the target strength. Water to add equals the final volume minus the starting volume. For 1 L at 57 % ABV, the batch holds 570 mL of alcohol, the final volume at 40 % is 1,425 mL, so you add 425 mL (14.37 fl oz) of water.
How do I dilute cask strength whiskey to bottling strength?
Enter the cask strength as the starting strength and your bottling strength as the target, then read “Water to add”. For 1 US gal at 120 proof (60 % ABV) cut to 80 proof (40 % ABV), the final volume is 1.5 gal, so you add 0.5 gal (1.893 L) of water.
How do I mix two spirits to get a target ABV?
Use Blend mode. Spirit A equals the total volume times (target minus B), divided by (A minus B). Spirit B equals the total volume minus spirit A. For 750 mL at 60 % ABV from a 95 % spirit and a 40 % spirit, you need 272.7 mL (9.222 fl oz) of the 95 % spirit and 477.3 mL (16.14 fl oz) of the 40 % spirit.
What is a proof gallon and how do I calculate it?
A proof gallon is a US gallon of liquid at 100 proof (50 % ABV) at 60 °F, or its alcoholic equivalent (27 CFR 5.1). So proof gallons equal US gallons times proof, divided by 100. For 53 gal at 62.5 % ABV (125 proof), the result is 66.25 proof gallons. The figure is an estimate; tax or legal numbers must come from your own gauge records.
Sources
- 27 CFR 5.1 (eCFR) — TTB definitions: proof is twice the percentage of ethyl alcohol by volume at 60 °F; a proof gallon is a gallon at 60 °F containing 50 percent alcohol by volume, or the alcoholic equivalent
- 27 CFR 30.11 (eCFR) — the same proof definition in the TTB Gauging Manual rules
- 27 CFR 30.1 (eCFR) — lists the Gauging Manual tables for hydrometer temperature correction (Table 1, 0 to 100 °F) and the volumes of alcohol and water at each proof (Table 6)
Worked examples
| Input | Result |
|---|---|
| 40 % ABV | 40 % ABV / 80 proof |
| 151 proof | 75.5 % ABV / 151 proof |
| 1 L at 57 to 40 % ABV | add 425 mL (14.37 fl oz) of water |
| 1 gal at 120 to 80 proof | add 0.5 gal (1.893 L) of water |
| 750 mL: 95 and 40 to 60 % ABV | 272.7 mL (9.222 fl oz) of A and 477.3 mL (16.14 fl oz) of B |
| 53 gal at 62.5 % ABV | 66.25 proof gallons |
Calculated by the tool above with these values.
Frequently asked questions
Is US proof the same as UK proof?
No. US proof is twice the % ABV at 60 °F. This page works with US proof only.
Do I need a hydrometer after diluting?
For a quick estimate, the ideal figures may be enough. For exact work, check the batch with a hydrometer at the right temperature. The tool’s warnings point to TTB Gauging Manual Table 1 (27 CFR 30.1), which is used to correct hydrometer readings for temperature.
Why is my diluted spirit stronger than the calculator says?
Water and alcohol shrink slightly when mixed, so the real batch is a little smaller and a little stronger than the simple balance. The calculator applies no contraction factor. For exact figures, use a hydrometer reading and the TTB Gauging Manual tables, including Table 6.
What is 100 proof in ABV?
100 proof is 50 % ABV, since proof is twice the percent alcohol by volume.
Is the calculator free, and is anything I type uploaded?
Yes, the calculator is free and runs in your browser with no sign-up. Nothing you type is uploaded.
How much water do I add to dilute 1 litre of 57 % spirit to 40 %?
About 425 mL. The alcohol balance keeps 570 mL of alcohol, so the batch has to grow to 1.425 L at 40 % ABV (80 proof). Because the mix contracts slightly, add a little less first and check with a hydrometer.
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