Alcohol by Volume (ABV) Calculator

What is an ABV calculator?

An alcohol by volume (ABV) calculator estimates how strong a fermented drink is from two hydrometer readings: the original gravity (OG) measured before fermentation and the final gravity (FG) measured after it. As yeast turns sugar into alcohol and carbon dioxide, the liquid gets lighter, and the size of that drop tells you how much alcohol was produced.

ABV is the standard way strength is reported on beer, wine, and spirits labels — a 5% ABV beer is 5% alcohol by volume. This tool is aimed at home brewers, winemakers, and mead makers who want a quick strength estimate from their own gravity readings.

How does it work?

Specific gravity is the density of a liquid compared with water, so it is a dimensionless number with no units. Pure water reads $1.000$; sugary wort or must reads higher because dissolved sugar makes it denser.

• Original gravity (OG) is taken before you pitch the yeast — a typical beer sits around $1.040$ to $1.060$.
• Final gravity (FG) is taken once fermentation finishes — usually $1.005$ to $1.015$ once most of the sugar is gone.

The difference between the two, multiplied by a constant, gives the approximate ABV. The calculator also reports alcohol by weight (ABW), which is lower than ABV because alcohol is less dense than water.

Formula

The widely used homebrew approximation is:

$\text{ABV}\% = (OG - FG) \times 131.25$

Alcohol by weight follows from the density ratio of ethanol to water:

$\text{ABW}\% = \text{ABV}\% \times 0.79336$

Where:

• $OG$ = original gravity (dimensionless), measured before fermentation
• $FG$ = final gravity (dimensionless), measured after fermentation

The factor $131.25$ is an empirical constant that works well for the gravity ranges common in beer and wine. If the final gravity is higher than the original gravity, fermentation has not lowered the density and the calculator returns no result.

Worked examples

Example 1 — a standard ale. OG $1.055$, FG $1.010$:

$\text{ABV}\% = (1.055 - 1.010) \times 131.25 = 5.91\%$

$\text{ABW}\% = 5.91 \times 0.79336 \approx 4.69\%$

Example 2 — a slightly stronger batch. OG $1.060$, FG $1.012$:

$\text{ABV}\% = (1.060 - 1.012) \times 131.25 = 6.30\%$

$\text{ABW}\% = 6.30 \times 0.79336 \approx 5.00\%$

Example 3 — a lighter session beer. OG $1.048$, FG $1.010$:

$\text{ABV}\% = (1.048 - 1.010) \times 131.25 \approx 4.99\%$

Practical notes

• Temperature correction matters. Hydrometers are calibrated to a specific temperature (often 20 °C / 68 °F). A reading taken on warm wort will be off, so let samples cool or apply your hydrometer’s correction chart.
• The 131.25 factor is an approximation. More elaborate formulas fit high-gravity beers and wines better, but $(OG - FG) \times 131.25$ is accurate to within a few tenths of a percent for most homebrew batches.
• Watch your sugar additions. Priming sugar added at bottling ferments in the bottle and adds a small amount of extra alcohol not captured by a pre-bottling FG reading.
• ABV vs. ABW. Some regions historically labelled drinks by weight. Because ethanol is about 0.79 times as dense as water, ABW is always the smaller number.

If you are planning a batch, our gallons to milliliters and liters to ounces converters help you scale recipe volumes, and the BAC calculator shows how that finished strength translates into blood alcohol content.

FAQ

What is the difference between OG and FG? Original gravity (OG) is the density of your unfermented wort or must; final gravity (FG) is the density after fermentation. The gap between them reflects the sugar the yeast converted into alcohol.

Why is ABW lower than ABV? Alcohol is less dense than water, so a given volume of alcohol weighs less than the same volume of water. That makes the percentage by weight smaller than the percentage by volume.

Do I need to correct for temperature? For accurate results, yes. Hydrometers are calibrated to a reference temperature, and readings taken warmer or colder need adjustment using the correction chart supplied with your instrument.

Can I use this for spirits? This formula is designed for the gravity range of beer, wine, and mead. Distilled spirits change alcohol content during distillation, so their strength is measured directly with an alcoholmeter rather than from gravity.