Brix to Specific Gravity Converter: Refractometer and Hydrometer Tool

What Brix, Specific Gravity and Plato Measure in Homebrewing Wort

A meadmaker in Nashville measures her honey must with a refractometer before pitching. The reading is 22.5 Brix. She converts it: SG equals 1 plus 22.5 divided by (258.6 minus 227.1 times 22.5 divided by 258.2), which equals approximately 1.094. That is her original gravity. She records it in her brew log alongside 22.5 degrees Plato (Brix and Plato being essentially identical for this purpose). Four weeks later, the refractometer reads 8.2 Brix. She knows this is not the actual FG because alcohol skews refractometer readings. She enters 22.5 OG Brix and 8.2 FG Brix into the Novotny refractometer correction and gets a corrected FG of approximately 1.003, giving an ABV of approximately 11.9 percent. She verifies with a hydrometer and reads 1.004 the accuracy is close enough to confirm fermentation is nearly complete.

Brix, specific gravity, and degrees Plato all describe the same underlying property of wort or must: the concentration of dissolved sugars. They just express it on different scales for different historical and professional contexts. Brix and Plato are percentage-based (grams of sugar per 100 grams of solution). Specific gravity is density-based (density relative to water). All three are related by the same physical chemistry, and this calculator converts between all three directions with the most accurate formulas available for each conversion.

Why the Refractometer Fails After Fermentation

A refractometer works by measuring how much a liquid bends (refracts) light. Dissolved sugars increase refraction. But alcohol also increases refraction, though by a different amount per gram than sugar does. Before fermentation, the dissolved material is almost entirely sugar, so the refractometer reading is accurate. After fermentation begins, alcohol replaces some sugar. The refractometer reads the combined effect of remaining sugar and alcohol on light refraction. Since alcohol affects refractive index differently than sugar, the raw Brix reading is no longer a direct measure of sugar concentration. Without correction, you overestimate the SG and underestimate how far fermentation has progressed. The Novotny cubic correction accounts for this by modeling the alcohol-sugar-water ternary mixture.

How This Converter Works: Three Modes for Every Brewing Situation

Mode 1: Brix to SG (Most Common for Refractometer Users)

Enter your Brix reading to get SG, degrees Plato, gravity points, and potential ABV (for fully dry fermentations). The wort correction factor (WCF) input adjusts for the difference between your refractometer’s sucrose calibration and actual wort composition. Most refractometers used for beer wort need a WCF between 1.02 and 1.04. If you do not know your WCF, leave it at 1.000 and calibrate it by comparing a refractometer reading to a hydrometer reading of the same wort sample.

Mode 2: SG to Brix and Plato

Enter a hydrometer SG reading to get the equivalent Brix, degrees Plato, and gravity points. This is useful when your recipe software outputs SG but your measurement instrument reads Brix, or when you want to know the professional Plato equivalent of a recipe OG. Uses the ASBC cubic polynomial, which is more accurate than the simple linear approximation at high and low gravity extremes.

Mode 3: Hydrometer Temperature Correction

If your wort sample is not at the hydrometer’s calibration temperature (usually 60 degrees Fahrenheit), your reading is inaccurate. Hot wort is less dense than it is when cool, so the hydrometer floats higher, giving a falsely low SG. Cold wort is denser, giving a falsely high SG. This mode uses the ASBC water density polynomial to compute the exact correction. Enter your raw reading, sample temperature, and calibration temperature (60 degrees Fahrenheit for most US hydrometers, 68 degrees Fahrenheit for some European models).

Mode 4: Refractometer Post-Fermentation Correction (Novotny)

Enter the original Brix reading taken pre-fermentation and the current Brix reading from the refractometer during or after fermentation. The Novotny cubic correction formula computes the corrected SG FG, degrees Plato of the FG, and the estimated ABV. The result also shows the corrected OG in SG for reference. This correction handles all the complexity of alcohol’s effect on refractive index in a single formula.

Three Real US Homebrew Measurement Scenarios Using Brix and SG

Expert Tips for Accurate Gravity and Refractometer Readings in Homebrewing

Find Your Refractometer’s Wort Correction Factor Once, Use It Always

Your refractometer’s wort correction factor is specific to your instrument and is the most important calibration step for accurate brewing measurements. Take a wort sample at any point before fermentation begins. Read the Brix from the refractometer. Immediately take a hydrometer reading of the same sample (temperature-corrected if needed). Convert the hydrometer SG to Plato using the ASBC cubic formula, then divide by the refractometer Brix reading. The result is your WCF. Example: refractometer reads 12.4 Brix, hydrometer reads 1.048 SG which converts to 11.93 degrees Plato. WCF equals 11.93 divided by 12.4 equals 0.962. Record this permanently for your instrument.

Calibrate Your Refractometer With Distilled Water Before Every Session

Temperature changes cause refractometer calibration to drift. Place two drops of distilled water on the prism, close the cover, and point toward a light source. The shadow line should fall exactly at 0.0 Brix. If it does not, adjust the calibration screw. Distilled water, not tap water, is essential because dissolved minerals in tap water shift the reading slightly. Recalibrate every brew session and any time the ambient temperature has changed significantly since the last calibration. Temperature-compensated (ATC) refractometers handle some of this automatically but still benefit from regular zero-point verification with distilled water.

Use Hydrometer Temperature Correction for All Hot Wort Readings

Many homebrewers skip temperature correction because it seems like a small detail. The reality: at 100 degrees Fahrenheit, the correction can be as large as 0.010 SG, which is a significant difference between apparently hitting your OG target versus being 10 gravity points off. This is especially important for all-grain brewers checking pre-boil or post-sparge gravity when the wort is still hot from the mash. A thermometer alongside your hydrometer and this temperature correction calculator eliminates a systematic error that many brewers carry into every batch without realizing it.

Quick Reference: Brix, Plato and SG Conversion Table for US Homebrewers

Brix to SG using formula SG = 1 + Brix / (258.6 minus 227.1 times Brix / 258.2). Plato from ASBC cubic polynomial. Source: American Society of Brewing Chemists (ASBC) Method Beer 1.

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