Input
How to use this calculator
Enter the Original Gravity (OG) measured before fermentation and the Final Gravity (FG) measured after fermentation has finished. Use specific gravity values such as 1.050 and 1.010, not Plato or Brix. A hydrometer reading should be temperature-corrected when the sample is not at the instrument calibration temperature.
Use the calculator after you have stable readings. If gravity is still falling, the result is only provisional. The volume field is included to put the result in context, but the current ABV estimate is derived from OG and FG rather than volume.
How the calculation works
This calculator uses the same higher-gravity ABV equation as Beer Control: ABV = (76.08 x (OG - FG) / (1.775 - OG)) x (FG / 0.794). It estimates the alcohol created by the reduction in specific gravity; it is not a laboratory alcohol measurement and does not model every fermentation by-product.
OG represents wort density before yeast activity. FG represents the density remaining after fermentation. The difference is affected by fermentability, yeast performance, temperature control and measurement quality. Do not enter a Plato value in an SG field.
Example calculation
With OG 1.050 and FG 1.012, the calculator returns approximately 5.1% ABV. The result is an estimate of alcohol by volume based on the measured density change.
Understanding the result
ABV is useful for comparing a batch with its recipe target, checking fermentation progress and planning packaging. It is derived from gravity readings, so a wrong OG, an unstable FG or an uncorrected hydrometer reading will affect it directly.
Treat the result as an estimate. Real alcohol content can differ because gravity readings include dissolved compounds other than fermentable sugar. For repeatable brewing, record the readings and use the same measurement method each time.
Common mistakes
- Entering Plato or Brix instead of specific gravity.
- Using an FG taken before fermentation is stable.
- Ignoring sample temperature correction.
- Comparing readings taken with different instruments without checking calibration.
Frequently asked questions
What is the difference between OG and FG?
OG is the wort density before fermentation; FG is the density after yeast has consumed part of the fermentable extract.
Can I calculate ABV without OG?
Not reliably with this method. The gravity change requires both a starting and finishing measurement.
Does temperature affect ABV?
Temperature affects gravity readings. Correct the readings before entering them so the estimated alcohol is based on comparable values.
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