Alcohol by Volume ABV Calculator

How to use the abv calculator

1. Measure the original gravity (OG) of your wort or must with a hydrometer or refractometer before pitching yeast.
2. After fermentation is complete, measure the final gravity (FG).
3. Enter both values into the fields above; the result updates instantly.
4. Read the calculated alcohol by volume percentage along with apparent attenuation and gravity drop.

How the ABV formula works

The standard equation used by homebrewers to find alcohol by volume is straightforward:

ABV = (OG - FG) x 131.25

The constant 131.25 converts the change in specific gravity into a percentage of ethanol by volume. It accounts for the density difference between sugar water and alcohol. For example, if your original gravity is 1.050 and your final gravity is 1.010, the math is: (1.050 - 1.010) x 131.25 = 0.040 x 131.25 = 5.25%.

This formula gives an approximation that is highly accurate for beers under 10% ABV. For very high-gravity fermentations like barley wines, more complex equations exist, but the standard formula remains the most widely used in homebrewing.

Understanding specific gravity

Specific gravity measures the density of a liquid relative to pure water, which has a gravity of exactly 1.000. Dissolved sugars make the liquid denser, raising the reading above 1.000. As yeast consumes those sugars and produces ethanol (which is lighter than water), the gravity drops.

A hydrometer floats lower in finished beer than it did in unfermented wort because alcohol reduces the overall density. This is why final gravity can sometimes fall below 1.000, particularly in dry ciders or highly attenuated Belgian ales.

Always take readings at the temperature your instrument was calibrated for, typically 60°F (15.6°C) or 68°F (20°C). Temperature variations skew the density of the liquid and produce inaccurate results.

Common gravity ranges by style

Different beer styles target different starting and ending gravities. Here is a reference table of typical values and the resulting alcohol by volume:

These are guidelines. Your actual numbers will depend on the grain bill, mash temperature, and yeast strain you choose.

Apparent vs real attenuation

Attenuation describes what percentage of sugars the yeast consumed. The alcohol by volume ABV calculator also shows apparent attenuation, computed as (OG - FG) / (OG - 1) x 100. For an OG of 1.050 and FG of 1.010, that is 0.040 / 0.050 x 100 = 80%.

This figure is called "apparent" because the presence of alcohol, which is less dense than water, makes the final gravity read lower than it would if only water and residual sugars were present. "Real" attenuation corrects for this effect and is always a few points lower. Most brewers track apparent attenuation because yeast manufacturer specifications use it.

If your measured attenuation falls far outside the expected range for your yeast strain, fermentation may be stuck, or your original gravity reading may have been taken when the wort was too hot.

Practical tips for accurate readings

Getting reliable numbers from this tool depends entirely on the quality of your measurements. Follow these practices to avoid common mistakes:

• Degas the sample. Carbon dioxide bubbles cling to a hydrometer and lift it, giving a falsely high final gravity reading. Stir the sample vigorously or pour it back and forth between two glasses before measuring.
• Use a refractometer carefully. Refractometers measure how light bends through a liquid. Once alcohol is present, the refraction changes in ways the scale does not account for. You must apply a correction formula to use a refractometer for final gravity.
• Record temperatures. If your wort is at 80°F but your hydrometer is calibrated for 60°F, the reading will be off. Use a temperature adjustment chart or let the sample cool first.

Accurate inputs ensure the calculated alcohol by volume reflects reality rather than measurement error.

Worked examples

Each result below was produced by the same code the tool runs, so you can check your own numbers against them.