How to use it
- Type the Original gravity (before fermentation) from your reading taken before the yeast was added.
- Type the Final gravity (after fermentation) from your reading of the finished beer.
- Read the Alcohol by volume, standard formula (%), the usual homebrew estimate.
- Compare it with the Alcohol by volume, second formula (%). The two formulas can give different results.
How the standard formula works
Specific gravity compares the density of a liquid with that of water. Yeast turns sugar into alcohol and carbon dioxide, so the gravity falls during fermentation. The fall, from the original to the final gravity, is multiplied by a fixed constant to give the alcohol by volume. The Brewday documentation calls this the basic formula that most brewing sites use.
ABV = (OG − FG) × 131.25
OG original gravity, for example 1.050
FG final gravity, for example 1.010- Both readings must be specific gravity, not Plato or Brix readings.
- The result is a percentage of volume, the same kind of figure as a label.
The second formula and where it comes from
The Brewday library also gives a second formula, which it attributes to Ritchie Products (Zymurgy, Summer 1995) and to Daniels' book Designing Great Beers. The page shows both so that you can compare them. Neither is a measurement of the alcohol in your beer.
ABV = (76.08 × (OG − FG) ÷ (1.775 − OG)) × (FG ÷ 0.794)What this calculator does not cover
- Readings from a refractometer or from a diluted sample. Convert them to specific gravity first.
- Sugar or fruit added after the first reading, which changes the starting gravity.
- A measurement of the alcohol itself, and any legal or tax figure.
Worked example: 1.050 to 1.010
The gravity falls by 1.050 − 1.010 = 0.040. The standard formula gives 0.040 × 131.25 = 5.25 %.
The second formula gives 76.08 × 0.040 ÷ (1.775 − 1.050) × (1.010 ÷ 0.794) = 5.34 %.
| Formula | ABV (%) |
|---|---|
| Standard | 5.25 |
| Second | 5.34 |
Frequently asked questions
What is original gravity?
It is the specific gravity of the wort before fermentation, the sweet liquid that becomes beer. A reading of 1.050 means the liquid is about 5 % denser than water.
Why do the two formulas give different answers?
Both are approximations built on different assumptions. The Brewday documentation names the source of each, so you can read where the second formula comes from.
Can I use this calculator for wine or cider?
The formulas are written for brewing wort. For other drinks the result is at best a rough estimate, and this page does not check it.
Is this the alcohol content printed on a label?
Not necessarily. A label shows the brewer's own figure, found by the brewer's method. This page gives a homebrew estimate from two gravity readings.
Sources
Figures and text last checked on Thursday, November 12, 2026.