# ABV Calculator (Alcohol by Volume)

If you want to calculate the alcohol content of your homebrewed beer, this ABV calculator (alcohol by volume calculator) is a perfect tool for you. It will help you estimate the percentage of alcohol in any liquor basing on its initial and final specific gravity. Use it wisely, and try not to fall into addiction! :)

## Calculating ABV from specific gravity

The standard method of estimating ABV is to use the specific gravity. Specific gravity is the relative density of a liquid compared with the density of water. When fermentation occurs, the specific gravity of a spirit changes. You can monitor this change to find the alcohol content of your homebrew.

All formulas for finding the ABV are approximate, as they are found empirically rather than derived. You should always expect some error when using the alcohol calculator. The most popular equation is:

`ABV = (OG - FG) * 131.25`

where:

- ABV is the alcohol by volume, measured in percents;
- OG is the original specific gravity (before fermentation), measured with a hydrometer;
- FG is the final specific gravity (after fermentation).

You can also use this specific gravity calculator to recalculate this result into alcohol by weight. All you have to do is apply the following formula:

`ABV = ABW / (0.789 + 0.211 * ABW)`

The last thing our beer calculator does is finding the exact amount of alcohol in a given volume of alcoholic beverage. For example, you can determine the volume of alcohol in a 500 ml bottle of 4.5% beer. If you are interested in finding this value, use this equation:

`alcohol volume = total volume * ABV`

## Difference between ABV, ABW and proof

Proof is a different measure of an alcoholic beverage. Its origins date back to 16th century England, where liquors were taxed basing on their alcohol content. They were tested in the following way: a pellet of gunpowder was soaked in a spirit, and if it could still burn afterwards, the spirit was deemed above proof and taxed higher than ordinary.

In 1816, the gunpowder test was replaced with specific gravity test. Since then, the main measure of alcohol content was ABV (alcohol by volume) or ABW (alcohol by weight). Still, you can find the equivalent of proof in ABV:

- In the US, 'proof' is equal to twice the measure in ABV. For example, alcohol that is 100 proof has 50% ABV.
- In the UK, proof is defined as follows: "a quantity of 100 degrees proof liquor has the same weight as 12/13 of the same volume of pure water at 51°F." Hence, 100 proof alcohol has 57.15% ABV.

## Using our alcohol by volume calculator: an example

Let's assume you are brewing your own beer. What do you need to do to determine the volume of alcohol in one 330 ml bottle?

- Begin with calibrating your hydrometer. Check whether its reading for clear water is equal to 1. If not, you will have to adjust all consecutive readings.
- Take a hydrometer reading of your homebrew before fermentation begins. Let's assume this value - the original specific density - is equal to 1.060.
- Take a second hydrometer reading when your beer will be ready to drink. In this example we will assume the final specific gravity equal to 1.015.
- Input these values into the ABV formula:
`ABV = (OG - FG) * 131.25 % = (1.060 - 1.015) * 131.25 % = 0.045 * 131.25 % = 5.91 %`

- Once you have calculated the ABV, you can find the volume of alcohol in your beer by multiplying it by the total volume of homebrew in a bottle:
`5.91% * 330 = 19.5 ml`

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