Refractometer / Brix / SG / Plato Conversion Calculator

A refractometer reading in Degrees Brix converts into Specific Gravity (SG) and Degrees Plato, with a wort correction factor and an alcohol-adjusted reading covering the two stages where a raw refractometer number needs different handling: before fermentation, and after. A refractometer works by bending light through a drop of liquid rather than measuring buoyancy the way a hydrometer does, which is exactly why alcohol, invisible to a hydrometer's weight-based reading, throws off a refractometer's post-fermentation number unless it is corrected for separately. Three modes cover the full brewing workflow.

Pre-Fermentation mode corrects a raw refractometer Brix WRI reading into actual Brix, Plato, and Specific Gravity values, dividing by the wort correction factor (default 1.04) before converting to Specific Gravity using the ASBC polynomial. Post-Fermentation mode takes both an OG and an FG refractometer reading and applies the Novotny correction formula, from Zymurgy (July/August 2017), to account for the alcohol refraction error that a raw refractometer reading cannot see on its own, returning corrected OG, corrected FG, ABV, and apparent attenuation. Direct Conversion mode converts a single value between Brix, Plato, and SG without any wort correction, useful when the value is already a true gravity reading rather than a raw refractometer number.

Settings holds the wort correction factor, adjustable from its 1.04 standard when a specific refractometer or wort composition calls for a different value, along with the number of decimal places shown for Specific Gravity output.

Refractometer readings convert into brewer-friendly gravity units across the full brewing workflow, from mash efficiency checks through final gravity measurement and ABV estimation.

• Brew Day Efficiency: A quick refractometer reading of first runnings or pre-boil wort, converted from Brix WRI to Specific Gravity, calculates mash or brewhouse efficiency on the fly without cooling a full hydrometer sample.
• Fermentation Monitoring: Both OG and a current refractometer reading, entered in Post-Fermentation mode, track fermentation progress; the alcohol correction formula gives an accurate current gravity estimate without pulling a large sample from the fermenter.
• Final Gravity and ABV: Final ABV and apparent attenuation at the end of fermentation can be determined using only a refractometer, with the result compared against hydrometer readings to validate a specific wort correction factor.
• Winemaking: Brix readings from grape must convert to Specific Gravity for recipe formulation and potential alcohol estimation, adjusting the wort correction factor to match a specific refractometer and must composition.
• Recipe Development: Target gravity values convert between Brix, Plato, and SG when following recipes from different brewing traditions, since European recipes often specify Plato while American home brew recipes use SG.
• Refractometer Calibration: Corrected refractometer readings compared against hydrometer measurements across multiple worts determine an instrument's specific wort correction factor for improved accuracy.
• Professional Brewing: Degrees Plato, used in continental European and professional brewing, converts with Specific Gravity, common in American and British home brewing, for communication across brewing communities and documentation standards.
• Education: The relationship between sugar concentration scales becomes visible in Direct Conversion mode, with the underlying formulas showing how Brix, Plato, and SG relate mathematically.