# What is my brew’s ABV?

Computes the alcohol by volume of beer, wine, cider or mead from the original and final specific gravity, by the standard formula or the alternate formula for strong brews, with alcohol by weight and apparent attenuation.

- Page: https://www.acalculator.org/food/abv-calculator
- JSON spec: https://www.acalculator.org/food/abv-calculator.json
- Version: b418022f0425

## Default answer

Example with the default inputs (Original gravity (OG) 1.05, Final gravity (FG) 1.01, Formula Standard): From 1.05 down to 1.01, the ABV is 5.25%.

## Inputs

| Key | Label | Description |
| --- | --- | --- |
| og | Original gravity (OG) | The specific gravity before fermentation, such as 1.050. |
| fg | Final gravity (FG) | The specific gravity after fermentation, such as 1.010. |
| formula | Formula | The standard formula, or the alternate formula that is closer for strong brews. |

## Outputs

| Key | Label | Description |
| --- | --- | --- |
| abv | Alcohol by volume | The alcohol as a percent of the volume. |
| abw | Alcohol by weight | The alcohol as a percent of the weight: ABV × 0.794 ÷ FG. |
| attenuation | Apparent attenuation | How much of the gravity above water fermented away: (OG − FG) ÷ (OG − 1). |

## Method

standard: ABV = (OG − FG) × 131.25; alternate: ABV = 76.08 × (OG − FG) ÷ (1.775 − OG) × FG ÷ 0.794; ABW = ABV × 0.794 ÷ FG

## Assumptions

- Gravities are specific gravities measured at the hydrometer’s calibration temperature, or corrected to it.
- Apparent attenuation uses the measured final gravity, which alcohol lowers, so it can pass 100% in a dry wine or cider.
- Sugar added after the original reading (priming or feeding) is not counted.

## Worked examples

1. og = 1.05, fg = 1.01, formula = standard gives abv = 5.25%, attenuation = 80%. Source: hand calculation in content.mdx: (1.050 − 1.010) × 131.25 = 5.25%; 0.040 ÷ 0.050 = 80%.
2. og = 1.05, fg = 1.01, formula = alternate gives abv = 5.339411%, abw = 4.197517%. Source: Hall, Brew by the Numbers, Zymurgy 18(2), 1995, as cited in content.mdx; hand calculation in content.mdx: 76.08 × 0.040 ÷ 0.725 = 4.198% ABW; × 1.010 ÷ 0.794 = 5.34% ABV.
3. og = 1.1, fg = 1.02, formula = alternate gives abv = 11.583409%. Source: hand calculation in content.mdx: 76.08 × 0.080 ÷ 0.675 = 9.017; × 1.020 ÷ 0.794 = 11.58% (standard: 10.50%).
4. og = 1.09, fg = 0.995, formula = standard gives abv = 12.46875%, attenuation = 105.555556%. Source: hand calculation in content.mdx: 0.095 × 131.25 = 12.47%; 0.095 ÷ 0.090 = 105.6%.

## FAQ

### How do I calculate ABV from gravity?

Subtract the final gravity from the original gravity and multiply by 131.25. A beer that goes from 1.050 to 1.010 is 0.040 × 131.25 = 5.25% ABV.

### When should I use the alternate formula?

The standard formula is a straight line and reads low for strong brews. The alternate formula, from Michael Hall’s 1995 Zymurgy article, allows for the original gravity. For 1.100 down to 1.020 it gives 11.58% against the standard 10.50%. For normal beers the two are close.

### What is the difference between ABV and ABW?

ABV is the alcohol as a share of the volume; ABW is its share of the weight. Alcohol is lighter than water, so ABW is lower: ABW = ABV × 0.794 ÷ FG. A 5% ABV beer at FG 1.010 is about 3.9% ABW.

### What is apparent attenuation?

The share of the gravity above water that fermented away: (OG − FG) ÷ (OG − 1). It is apparent because alcohol is lighter than water, so the hydrometer reads lower than the sugar left; a dry wine can show more than 100%.

### Do I need to correct my hydrometer reading for temperature?

Yes, if the sample is not at the temperature the hydrometer is calibrated for (printed on it or in its instructions). Correct both readings first, then enter them here.

### What if I added sugar during fermentation?

The formula only sees the gravity change it is given. Sugar added after the original reading adds alcohol the readings do not show, so the result reads low.

## Sources

- Hall, M. L. (1995). Brew by the Numbers: Add Up What’s in Your Beer. Zymurgy, 18(2). Alternate formula ABV = 76.08 (OG − FG) ÷ (1.775 − OG) × FG ÷ 0.794.
- Brewday documentation, brew.utilities.abv: standard ABV = (OG − FG) × 131.25 and the alternate formula with its sources. https://brewday.readthedocs.io/en/latest/api/utilities/abv.html