ABV (Alcohol by Volume) Calculator

1. Take an original gravity reading before fermentation with a hydrometer.
2. Take a final gravity reading once fermentation is complete.
3. Enter both readings as decimals, such as 1.050.
4. Read the ABV, plus ABW, attenuation and standard drinks.

ABV, or alcohol by volume, is the standard measure of how strong an alcoholic drink is, shown as the percentage of the total volume that is pure alcohol. A 5 percent ABV beer means 5 percent of the liquid is ethanol. Homebrewers work it out from gravity readings, because measuring alcohol directly is difficult.

Specific gravity is the density of the liquid compared with water. As yeast eats sugar and makes alcohol, the gravity falls, and the size of that drop reveals how much alcohol was produced.

1. Subtract the final gravity from the original gravity.
2. Multiply the difference by 131.25, a constant that converts the gravity drop to percent alcohol.
3. Multiply ABV by 0.79 for alcohol by weight.
4. Divide the gravity drop by the original gravity drop above water for attenuation.

The 131.25 factor is the common brewing approximation. A slightly more precise formula exists for very strong brews, but 131.25 is accurate for typical beer, cider and wine.

A pale ale starts at an original gravity of 1.050 and finishes at 1.010. The gravity dropped by 0.040, so ABV is 0.040 times 131.25, which is 5.25 percent. Attenuation is 0.040 divided by 0.050, or 80 percent, meaning the yeast converted four fifths of the available sugar. A 12 ounce glass is about one standard drink.

Starting Sugar

More fermentable sugar raises the original gravity and the potential alcohol, which is why bigger beers start higher.

Yeast and Attenuation

Highly attenuative yeast eats more sugar, dropping the final gravity further and raising ABV, while low attenuation leaves a sweeter, weaker drink.

Fermentation Temperature and Time

Warm, healthy, complete fermentation reaches a lower final gravity; a stalled ferment leaves sugar behind and less alcohol.

Reading Accuracy

Hydrometers must be read at their calibration temperature, and trapped bubbles or a tilted sample skew the result.

Hydrometer vs Refractometer

A hydrometer floats in a sample and reads gravity directly, which is what this calculator expects. A refractometer measures how light bends through a drop and is handy for quick checks during the boil, but its final-gravity reading is thrown off by the alcohol already present. If you use a refractometer, convert its finished reading to true final gravity first, then enter that corrected value here so the ABV comes out right.

Different drinks sit in different strength ranges.

Cider spans a wide range, from about 4 percent for sweet styles to 8 percent or more for dry ones.

Brewing at Home

Check the strength of every batch of beer, cider, wine or mead you make.

Tracking Fermentation

Compare gravity readings over time to see whether fermentation has finished.

Serving Responsibly

Knowing the ABV and standard drinks helps you and your guests pace themselves and drink sensibly.

1. Reading Gravity Warm

Hydrometers are calibrated to a set temperature; a hot sample reads low.

2. Measuring Before Fermentation Finishes

An early final gravity overstates the sugar left and understates ABV. Wait for stable readings.

3. Confusing ABV and ABW

Alcohol by weight is lower than by volume; do not mix them up when comparing drinks.

4. Ignoring Attenuation

A high final gravity can signal a stuck ferment, not a finished one.

The 131.25 formula is the standard homebrew method and is accurate for typical strengths. Very high-ABV brews need a more complex formula.

ABV equals the original gravity minus the final gravity, multiplied by 131.25. For example, 1.050 down to 1.010 gives (0.040 x 131.25), which is 5.25 percent.

Original gravity is the density before fermentation, when sugar is high. Final gravity is the density after, once yeast has converted sugar to alcohol.

Most beers finish between 1.008 and 1.015, while dry ciders and wines can reach 1.000 or below. A stable reading over a few days means fermentation is done.

Attenuation is the share of sugar the yeast fermented, found from the gravity drop. Higher attenuation means a drier, stronger drink.

ABV measures alcohol by volume and ABW by weight. Because alcohol is lighter than water, ABW is about 79 percent of the ABV figure.

Common causes are a stuck fermentation, an inaccurate original gravity, or reading a warm sample. Confirm the ferment is finished and readings are at the right temperature.

Yes. The same gravity formula works for beer, cider, wine and mead, though very strong wines are slightly better served by a more advanced formula.

No. The calculator runs entirely in your browser and nothing you enter is stored or sent anywhere.

• Alcohol by volume explained (Wikipedia).
• Homebrewing and gravity (Wikipedia).
• Attenuation in brewing (Wikipedia).