Calculate alcohol by volume from original and final gravity readings, or find missing OG or FG with Specific Gravity, Plato, and US proof units.
Related Calculators
- Mead Alcohol Percentage Calculator
- Case Equivalent Calculator
- Wine Sugar Calculator
- Bitterness Ratio Calculator
- Brix To Grams Of Sugar Calculator
- All Food and Cooking Calculators
Alcohol by Volume (ABV) Formula
The calculator uses original gravity, final gravity, and alcohol by volume. Select Solve for, then enter the two known values. 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. Changing a unit converts the entered quantity. Results include the relevant equivalent units; the main ABV calculation uses specific gravity and ABV percent.
Typical ABV and Gravity Ranges
These are illustrative beverage ranges. The spirits row explains proof equivalence only; the hydrometer-difference formula is not suitable for determining distilled-spirit strength.
| 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 | Before fermentation, Plato approximates extract by mass. After fermentation, hydrometer-equivalent Plato is apparent extract and is not a direct sugar measurement. |
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. Equal readings produce a zero estimate, which does not certify an alcohol-free beverage. A final gravity above original gravity would produce a negative result and is rejected.
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. High-gravity fermentation may require a different model; this estimate is not a laboratory assay.
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.
