ABV calculator
Enter the specific gravity you measured before fermentation (OG) and after it (FG). You get the alcohol by volume and the apparent attenuation, using either the usual homebrew formula or a more accurate alternative.
Runs in your browser: nothing you enter is sent anywhere.
How to use it
- Enter the OG, measured before fermentation, as a specific gravity such as 1.050.
- Enter the FG, measured when fermentation has finished.
- Choose the standard or the alternative formula. The page also shows what the other one gives.
How it works
The standard formula multiplies the drop in gravity by 131.25. The alternative formula is 76.08 × (OG − FG) ÷ (1.775 − OG) × (FG ÷ 0.794); it adjusts the result for higher gravities, where the standard formula tends to read low.
Worked example
OG 1.050 and FG 1.010. Standard: (1.050 − 1.010) × 131.25 = 0.04 × 131.25 = 5.25% ABV. Alternative: 76.08 × 0.04 ÷ 0.725 × (1.010 ÷ 0.794) = 5.34%. Attenuation: 0.040 ÷ 0.050 = 80%.
Tips
- Take the FG on two days in a row: if it has not changed, fermentation has finished.
- Measure at the temperature your hydrometer is calibrated for, or correct for temperature.
- ABV from gravity is an estimate. Treat results with caution if you added sugar, fruit or other ingredients that change the density.
- Alcohol is also covered in blood alcohol content, a separate calculation.
Frequently asked questions
What is the formula?
The standard homebrew formula is ABV = (OG − FG) × 131.25. The alternative is ABV = 76.08 × (OG − FG) ÷ (1.775 − OG) × (FG ÷ 0.794). The two agree closely for ordinary beers and drift apart at higher gravities, where the alternative is considered more accurate.
Which formula should I use?
For beer around 1.040 to 1.060 the difference is small, as the "other formula" line shows. For strong beer, wine or mead with a high OG, use the alternative formula. Both are estimates from hydrometer readings, not lab results.
What are OG and FG?
Original gravity is the density of the liquid before the yeast is added, and final gravity is the density when fermentation has finished. Both are read with a hydrometer or refractometer and written as specific gravity such as 1.050. The sugar converted into alcohol lowers the density, and this is how the calculation works.
What is apparent attenuation?
The share of the original sugar that the yeast has used, worked out as (OG − FG) ÷ (OG − 1) × 100. An OG of 1.050 and FG of 1.010 gives 80%. It is called apparent because alcohol is lighter than water, which distorts the reading.
Can I enter readings in points or Plato?
This tool needs specific gravity written as 1.xxx. If your hydrometer gives points, put 1.0 in front: 50 points is 1.050. Degrees Plato and Brix are not supported here.