Beer Gravity Calculator

Beer gravity refers to the density of beer wort (unfermented beer) or beer relative to the density of water. It is measured using a hydrometer or refractometer and is expressed as a specific gravity (SG) reading — a number typically between 1.000 and 1.150. The specific gravity of pure water at 60°F is defined as 1.000, so wort with a gravity of 1.050 is 5% denser than water due to dissolved sugars from the malt.

Gravity readings are fundamental to brewing because they tell you how much sugar is present in the wort, which directly determines the potential alcohol content of the finished beer. The original gravity (OG) is measured before fermentation begins and indicates the total sugar content available for yeast to convert into alcohol and carbon dioxide. The final gravity (FG) is measured after fermentation is complete and indicates how much sugar remains unfermented.

The difference between OG and FG tells you how effectively the yeast fermented the available sugars. This difference is expressed as attenuation — the percentage of sugars that were consumed. Typical apparent attenuation ranges from 65% to 85%, depending on the yeast strain, fermentation temperature, and wort composition. Understanding gravity readings allows brewers to monitor fermentation progress, calculate alcohol content, and ensure their beer meets target specifications.

Several key formulas connect gravity readings to beer characteristics:

Brewers use several different scales to measure gravity, all expressing the same physical property:

All three scales measure the same thing — the concentration of dissolved sugars — but use different mathematical relationships. SG is a direct density ratio, while Plato and Brix are based on sugar content by weight. The calculator converts between these scales automatically.

Analyze your beer's fermentation characteristics in a few steps:

1. Enter Original Gravity (OG): Type the specific gravity reading taken before fermentation, typically between 1.030 and 1.120.
2. Enter Final Gravity (FG): Type the specific gravity reading taken after fermentation is complete, typically between 1.002 and 1.020.
3. Set batch size: Enter your batch volume and unit (gallons or liters) for fermentable estimates.
4. Optional: Enter Brix reading: If you measured in Brix instead of SG, enter the value to convert to specific gravity.
5. Review results: The calculator displays ABV, apparent and real attenuation, calorie content, and gravity conversions.

Monitoring fermentation is the primary use for gravity measurements. By taking periodic gravity readings, brewers can track the progress of fermentation and determine when it is complete. A stable FG reading over 2-3 days indicates that fermentation has finished and the beer is ready for packaging.

Recipe design relies on gravity calculations to achieve target ABV and flavor profiles. A brewer designing a 6% IPA needs to calculate the OG that will produce that alcohol level with their chosen yeast strain's typical attenuation. The calculator's ABV and attenuation tools make this planning straightforward.

Quality control in commercial breweries depends on consistent gravity readings to ensure each batch meets specifications. Deviations from target gravity can indicate problems with the mash, boil, or fermentation process, allowing brewers to identify and correct issues before the beer reaches consumers.