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Specific Gravity to Brix: Homebrewing Conversion Guide

Specific gravity and Brix are two different scales for measuring the same thing β€” dissolved sugar content in a homebrew β€” and both feed into estimating alcohol content.

Specific gravity compares density to water

Specific gravity (SG) is the density of a liquid relative to plain water, which is defined as exactly 1.000. Wort or must with dissolved sugar is denser than water, so a typical starting SG reads somewhere around 1.040 to 1.090 depending on the recipe.

Brix measures dissolved sugar as a percentage

Degrees Brix (Β°Bx) roughly represents the percentage of dissolved solids, mostly sugar, by weight. A reading of 15Β°Bx means roughly 15% of the liquid's weight is dissolved sugar and related solids.

OG and FG bookend fermentation

Original gravity (OG) is measured before fermentation starts, when sugar content is highest; final gravity (FG) is measured after fermentation finishes, once yeast has converted most of the sugar to alcohol and CO2, so FG is always lower than OG.

A simple ABV formula from OG and FG

A common quick estimate is ABV β‰ˆ (OG βˆ’ FG) Γ— 131.25, using gravity in the 1.0XX format (so 1.050 becomes 0.050 for the subtraction). More precise formulas exist for higher-gravity brews, where this simple version tends to overestimate slightly.

Refractometers need an alcohol correction after fermentation

A refractometer measures Brix optically and is fast and convenient, but once alcohol is present it skews the reading, so a correction formula (or a separate hydrometer reading) is needed for an accurate FG once fermentation is underway.

Why brewers track both scales

Brix is intuitive as a sugar percentage and is standard in winemaking and fruit-based brewing, while SG has a long history in beer brewing recipes and hydrometer equipment. Many brewers end up needing to convert between the two depending on which instrument or recipe tradition they are working from.

Temperature affects both readings

Hydrometers and refractometers are typically calibrated for a specific reference temperature, often 20Β°C (68Β°F). Taking a reading from a hot or cold sample without correcting for temperature introduces a real error, which is why many brewing calculators include a temperature correction step.

Frequently Asked Questions

Is Brix or specific gravity more accurate for estimating ABV?

Neither is inherently more accurate β€” they measure the same dissolved-solids property on different scales, and standard conversion formulas move reliably between them. Accuracy mostly comes down to correct temperature calibration and taking OG before yeast is pitched.

Why does my final gravity refractometer reading seem too high?

That's the classic alcohol-skew problem β€” a refractometer reads sugar and alcohol together and overstates remaining sugar once alcohol is present, so raw refractometer FG readings need an alcohol-correction formula to be usable for ABV math.