## What Is Alcohol by Volume?

Alcohol by volume or ABV is the most common metric which is used to measure the alcoholic strength of a drink.

It can be used to express the alcoholic content of a beer, wine, or type of spirit and is commonly found displayed on the label as a percentage. The measurement will show what percentage of the beverage’s total volume is pure alcohol.

If you are setting up a new bar or starting to brew your own beers for sale it can be important to know the strength of an alcoholic drink as it can affect the taste of the drink or the capacity for how much somebody can drink before becoming intoxicated.

## ABV Labelling and the Federal Law

Not all beers have ABV stated on their labels though! In most States it is optional, and even forbidden in some!

This “optional” ABV labeling of beers dates back to a law passed by Congress in 1935 after the repeal of prohibition where the authorities hoped to prevent “strength wars” by the brewers assuming customers would go for the strongest beers.

At the moment Federal Law leaves it up to the individual states on whether a brewer must display their ABVs, which has resulted in a mixed-up confusion of state and federal laws on ABVs.

For example, New York currently prohibits the labels including the ABV while states like North Carolina, Washington, and New Hampshire dictate beers over 6 percent, 8 percent, or twelve percent must be labeled accordingly.

## Why Do I Need to Know the ABV of My Beer Then?

If you are brewing beer for your own personal consumption, then, strictly speaking, there is no need to know the ABV. But, as we stated earlier, the alcoholic content of a beer can affect the taste and flavors of a recipe.

If you want a consistent flavor to your beer, understanding the ABV can help make sure it’s the same beer every time.

If you are inviting beer-drinking buddies over to sample your homebrewed beers they may want to know the ABV so they know just how many they can drink in a session before falling over, or even just to ensure they are safe to drive home.

And finally, craft beer drinkers are always demanding more and more information about the beers they are drinking. Not just the ingredients used, the hops added, and the processes involved in brewing, but also the ABV and the potential health benefits of understanding the ABV.

Just as lager drinkers have now favored the Lite beers market, many craft beer drinkers are looking for more sessionable beers, even Session IPAs, with a lower ABV.

## Calculating ABV Using Specific Gravity Values

The most common way for calculating how much pure alcohol is in a beverage is to measure the difference in specific gravities, namely the original starting specific gravity of a brew and the final specific gravity of the finished beer or spirit.

A gravity value measurement can be read using a hydrometer or refractometer both before and after the fermentation of the liquid.

The original starting gravity measurement reads the density of fermentable sugars in the wort before fermentation.

As the density of sugar in the water is greater than that of alcohol, by measuring the specific gravity after fermentation you can calculate the volume of alcohol which is in the liquid.

Although we have included an ABV Calculator brewing tool, you could always use the simple ABV formula below to calculate your ABV, if you don’t mind doing it longhand.

The original formula or standard equation as used by most homebrewers is:

Original Gravity = Original gravity reading taken with a Hydrometer before you pitch the yeast

Final Gravity = The hydrometer reading after fermentation is complete.

131.25 = The conversion factor for the relative density of alcohol and water as reached through the use of biochemistry calculations.

For expert brewmasters, there are more exact formulae that use a more precise ABV equation, but let our calculators for beer do all the work for you…..it is pretty complex but here goes:

## The Difference Between ABV and Proof

Although Alcohol by Volume ABV is the method used to most commonly state the alcoholic strength of a drink, you may have often seen the alcohol content expressed as “Proof”.

In the US it’s quite easy to grasp the difference between proof and ABV, as Proof is basically double the percentage of alcohol by volume.

So for example 80-proof spirits are a spirit that contains 40 % alcohol by volume.

Proof is mainly used to display the alcohol content of spirits and dates back to the bootlegging days when traders would often water down their spirits.

To “prove” the alcoholic strength they would have to mix their spirits with gunpowder and if the spirit caught fire it was seen as “proof” the spirit was legitimate. Obviously, spirits with more alcohol ignited quicker and were seen as higher “proof”.

## Alcohol by Weight (ABW) vs Alcohol by Volume (ABV)

Although an ABV is what you will find most commonly on the labels in the US, in other regions of the world and some select areas of the States you may find the ABW or alcohol-by-weight.

Alcohol by weight is nearly always lower than the ABV at about 4/5 of the ABV. However, due to the miscibility of alcohol and water, the conversion factor is not always constant and changes depending on the concentration of alcohol.

At lower ABVs, there is a slight difference so that a beer that is said to be 5% alcohol by weight will actually be slightly above 5% ABV. At 0% and 100% ABV, it will be equal to the ABW but values in between will vary.

- ABV Difference to ABW Basic Equation
- ABW = (0.79 x ABV)/1.015

## Using Our ABV Calculator Tool

We have included a simple ABV calculator above to save you the hard work of long-hand mathematical equations.

It supports both Plato and Brix gravity measurements as well as the traditional Specific Gravity units.

Simply choose the gravity unit you will be using and then enter the original or starting gravity before the yeast is pitched and the final or end gravity after fermentation is complete.

Press calculate and the tool will give you the ABV of the liquid.

Remember, when using a hydrometer to take readings, the reading will need to be temperature corrected. Check out our Hydrometer Temperature Adjustment Calculator here.