Refractometer Brix to FG Calculator
Convert optical refractometer Brix readings into true Final Gravity, compensating for alcohol distortion.
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Why Refractometers Require Alcohol Correction
Refractometers are designed to measure refractive index changes in pure sugar solutions. However, ethanol possesses a refractive index of 1.3614 compared to water's 1.3330. As fermentation produces ethanol, the alcohol distorts the prism reading upward.
This calculator applies Sean Terrill's refined cubic model, converting original Brix and fermented Brix into the exact specific gravity you would observe on a calibrated glass hydrometer.
Frequently Asked Questions
Why can’t I read final gravity directly from a refractometer?
Because ethanol has a higher refractive index than water, it causes light to bend more sharply. A fermented beer will show 6° to 7° Brix even when fully attenuated to 1.010 SG.
What is Wort Correction Factor (WCF)?
Wort contains non-sugar solids, maltose, and complex dextrins that differ from the sucrose scale used to calibrate refractometers. A WCF of 1.00 to 1.04 scales the reading to true extract.
Is a refractometer better than a hydrometer?
A refractometer requires only 2 drops of liquid instead of 200ml, saving beer and eliminating cooling time. With software alcohol correction, it matches hydrometer precision.