How to Calculate the Alcohol Content (ABV) of Homebrewed Beer

Learn how to easily calculate the alcohol by volume (ABV) of your homebrewed beer. With tips on using online calculators and cheap tools.


Mat Stuckey

10/3/20233 min read

How to Calculate the Alcohol Content (ABV) of Homebrewed Beer

Determining the alcohol by volume (ABV) is an important step for any homebrewer looking to perfect their recipes and fermentation process. The ABV percentage indicates how much alcohol is present in the final beer. This guide will explain several methods to accurately measure the alcohol content of homemade brews.

What is ABV and Why Does it Matter?

ABV stands for alcohol by volume and is expressed as a percentage that represents the amount of ethanol alcohol within the beer. Knowing the ABV can help homebrewers:

  • Confirm that fermentation was complete and reached the proper final gravity.

  • Make adjustments to recipes for desired alcohol strength.

  • Identify issues if the ABV is higher or lower than expected.

  • Comply with alcohol tax and reporting regulations in some regions.

  • Provide consumers with alcohol information if selling homemade beer.

Accurately calculating ABV is an essential skill in brewing consistent, balanced beers.

Measuring ABV with a Hydrometer

One of the easiest ways to determine alcohol percentage is by using a hydrometer. This instrument measures the specific gravity (SG) of the wort before and after fermentation. Here are the steps:

  1. Take a hydrometer reading of the original pre-fermentation wort once yeast is pitched. This is your original gravity (OG).

  2. After active fermentation slows, take another hydrometer reading. This is your final gravity (FG).

  3. Plug the OG and FG values into an online ABV calculator or formula. It will provide the estimated ABV based on the change between gravities.

  4. Ensure wort is well mixed and the hydrometer is floating freely when taking readings. Repeat measurements to verify accuracy.

A hydrometer is an essential tool for determining ABV along with monitoring the stages of fermentation. However, good technique is required for precise readings.

Using Online ABV Calculators

For convenience, homebrewers can use one of the many online alcohol by volume calculators available. We have a free to use tool at Brewpedia here.

To use an online ABV calculator:

  1. Record your beer's original and final gravity readings from a hydrometer or refractometer.

  2. Select an appropriate calculator based on your gravity measurements.

  3. Carefully enter the OG and FG values into the calculator's fields.

  4. The tool will instantly output the estimated ABV percentage. Double check your inputs before calculation.

Online calculators eliminate manual formula work and provide quick, reliable ABV estimates. Just be sure gravity measurements are precise.

Calculating ABV from OG and FG Using a Formula

For those who prefer calculators, the alcohol by volume can be determined manually with a simple formula:

ABV = (OG - FG) x 131.25

To calculate:

  1. Use a hydrometer to measure and record the original gravity before pitching yeast.

  2. Once fermentation is complete, take a final gravity reading.

  3. Plug the OG and FG values into the formula above and multiply to estimate ABV.

  4. Round to the nearest whole number if needed.

This formula provides an accurate ABV percentage when your gravity readings are properly measured and recorded.

Getting Precise Gravity Readings for ABV Calculation

No matter which method you use, the accuracy of your original and final gravity measurements will directly impact the reliability of the calculated ABV.

Follow these tips for precision:

  • Carefully calibrate your hydrometer or refractometer.

  • Ensure wort samples are homogenised and free of air bubbles.

  • Read meniscus at proper angle and lighting.

  • Repeat readings 2-3 times and average for consistency.

With quality brewing equipment and good technique, homebrewers can dial in accurate ABV calculations.

Conclusion: Why Measuring ABV Matters

Knowing your beer's alcohol by volume percentage provides valuable insights into the fermentation process. While hydrometers, calculators, and formulas require some effort, they are essential tools for perfecting recipes, assessing fermentation, and improving your homebrewing skills. Start monitoring ABV today to produce consistent, balanced homemade beers.