Use this calculator to convert between Brix and specific gravity (SG), or to correct refractometer readings during fermentation.
What this refractometer calculator does
A refractometer estimates dissolved solids by measuring how much light bends as it passes through a liquid sample. In brewing, winemaking, kombucha, and food production, that number is usually shown in Brix (°Bx). This tool helps you quickly convert Brix to specific gravity (SG), convert SG back to Brix, and correct readings during fermentation where alcohol changes the optical behavior of the sample.
Why refractometer readings need correction after fermentation starts
Before fermentation, sugar dominates the sample, so Brix-to-SG conversion is straightforward. Once yeast produces alcohol, your raw refractometer reading becomes biased lower than the true sugar concentration because alcohol refracts light differently. That is why post-fermentation readings should be corrected with a formula that uses:
- Original Brix (before fermentation)
- Current Brix (during or after fermentation)
- A wort correction factor (optional but recommended for brewers)
This calculator uses a widely adopted empirical correction model to estimate final gravity (FG), then derives ABV and apparent attenuation.
How to use each mode
1) Brix to SG
Enter your Brix reading from fresh wort, juice, or solution. The calculator returns estimated specific gravity. This is ideal for pre-fermentation readings and recipe planning.
2) SG to Brix
If your process notes are in SG but your equipment reads in Brix, this mode gives a fast conversion for tracking and reporting.
3) Fermentation correction
Enter your original and current refractometer readings. Add a wort correction factor if you have calibrated your instrument (1.04 is a common brewing starting point). The calculator outputs:
- Estimated Original Gravity (OG)
- Estimated Final Gravity (FG)
- Estimated ABV (%)
- Apparent attenuation (%)
Practical tips for better accuracy
- Calibrate your refractometer with distilled water before use.
- Use a clean prism and take multiple readings to reduce random error.
- Let samples cool close to instrument calibration temperature (often 20°C / 68°F).
- Record original Brix at brew day start; it is essential for later alcohol correction.
- Treat ABV results as estimates unless verified with laboratory methods.
Formula notes
The conversion and correction equations used here are standard homebrewing approximations. They work well for everyday process control, but highly unusual matrices (high alcohol, high acidity, unusual sugars) may require lab-grade analysis.
Quick FAQ
Is Brix the same as Plato?
They are very close for many practical uses, but not mathematically identical in all conditions.
Can I use this for wine or cider?
Yes. The conversion modes work for many sugar-containing liquids. Fermentation correction is still an estimate.
What if I do not know my correction factor?
Start with 1.04 for beer wort and refine later by comparing against trusted hydrometer measurements.