Calculate alcohol by volume from original and final gravity readings, or find missing OG or FG with Specific Gravity, Plato, and US proof units.
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Alcohol by Volume (ABV) Formula
The calculator uses original gravity, final gravity, and alcohol by volume. You enter any two values, and it solves for the missing one. Gravity values are converted to specific gravity before the ABV formula is applied.
- ABV = alcohol by volume, as a percent
- OG = original gravity in specific gravity units
- FG = final gravity in specific gravity units
- 131.25 = common brewing conversion factor for estimating ABV from hydrometer readings
To calculate original gravity when final gravity and ABV are known, the calculator rearranges the same formula:
To calculate final gravity when original gravity and ABV are known, it uses:
If you choose U.S. proof instead of ABV percent, the calculator uses:
If you enter gravity in degrees Plato, the calculator converts Plato to specific gravity before using the ABV formula:
For converting specific gravity back to degrees Plato, it uses this approximation:
- SG = specific gravity
- P = degrees Plato
- Proof = U.S. proof, equal to twice the ABV percentage
Use the ABV mode when you have both hydrometer readings. Use the original gravity mode when you know the final gravity and target ABV. Use the final gravity mode when you know the starting gravity and ABV. Unit dropdowns only change how values are entered or displayed; the main ABV calculation is still based on specific gravity and ABV percent.
Typical ABV and Gravity Ranges
These ranges are general references for checking whether your result is in a normal range for common fermented drinks.
| Drink type | Typical ABV | U.S. proof equivalent |
|---|---|---|
| Light beer | 3% to 4.5% | 6 to 9 proof |
| Standard beer | 4.5% to 6.5% | 9 to 13 proof |
| Strong beer | 7% to 12% | 14 to 24 proof |
| Wine | 11% to 15% | 22 to 30 proof |
| Spirits | 35% to 50% | 70 to 100 proof |
| Reading | Typical beer range | What it means |
|---|---|---|
| Original gravity | 1.035 to 1.080 SG | Higher OG usually means more fermentable sugar and a higher possible ABV. |
| Final gravity | 1.006 to 1.020 SG | Lower FG usually means more sugar was fermented into alcohol. |
| Degrees Plato | About 9 to 19 °P for many beers | Plato estimates dissolved sugar by weight before or after fermentation. |
Examples
Example 1: Calculate ABV from original and final gravity
You have an original gravity of 1.060 and a final gravity of 1.012.
The estimated alcohol by volume is 6.30%. In U.S. proof, that is 12.60 proof.
Example 2: Calculate final gravity from OG and ABV
You have an original gravity of 1.070 and an ABV of 7.5%.
The estimated final gravity is 1.013 SG.
FAQ
Why does original gravity need to be higher than final gravity?
During fermentation, yeast converts sugar into alcohol and carbon dioxide. Since sugar increases density, the liquid usually starts with a higher gravity and ends with a lower gravity. If final gravity is equal to or higher than original gravity, the basic ABV formula gives zero or negative alcohol, which is not valid for a normal fermentation estimate.
Is this ABV result exact?
No. It is an estimate based on hydrometer-style gravity readings and the common factor 131.25. The actual alcohol content can vary because of temperature correction, instrument calibration, dissolved solids, fermentation byproducts, and the formula used. For typical homebrewing calculations, this estimate is usually close enough for practical use.
What is the difference between ABV and proof?
ABV is the percentage of a drink’s volume that is alcohol. U.S. proof is double the ABV percentage. For example, 40% ABV is 80 proof, and 6% ABV is 12 proof.
