Refractometer Alcohol Adj.

BrewCo Brew Tools

Alcohol in solution skews refractometer readings. This calculator corrects your final reading for an accurate ABV — using either specific gravity or Brix, whichever your refractometer reads in.

How to use it

  1. Take your original reading before fermentation (OG or original Brix).
  2. Take your final refractometer reading after fermentation.
  3. Choose the right tab for your refractometer's scale and enter both readings.
— % ABV
Fill in both fields above
— % ABV
Fill in both fields above

Why can't I just use a normal refractometer reading after fermentation?

Refractometers measure how light bends through a liquid, which changes with dissolved sugar — but alcohol also bends light, in the opposite direction to sugar. This makes a raw post-fermentation refractometer reading read too high unless corrected — which is exactly what this calculator does.

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Browse our range of refractometers and hydrometers at BrewCo UK.

Correcting refractometer readings after fermentation

What it does: a refractometer is accurate before fermentation, but once alcohol is present it reads too high. This calculator corrects your final reading so you get a true final gravity and ABV.

How to use it: choose the tab that matches how your refractometer reads, gravity (SG) or Brix. Enter your original reading, taken before fermentation, and the reading you have now. Use a couple of drops from a well-mixed sample.

The formula in plain words: the calculator converts both readings to Brix, then uses a standard correction formula that allows for the alcohol to estimate the true final gravity. ABV is then (OG − corrected FG) × 131.25.

Worked example: on the Brix tab, an original reading of 12.5°Bx and a final reading of 6.8°Bx. That gives an estimated OG of 1.050, a corrected FG of about 1.012 and an ABV of about 5.0%. Without the correction, the raw 6.8°Bx would look like a gravity of about 1.027 and you might think fermentation had stalled.

For a quick conversion of unfermented wort, use the Brix to gravity converter.

Frequently Asked Questions
Why does alcohol affect a refractometer?
A refractometer measures how much light bends as it passes through the liquid. Alcohol bends light too, so once fermentation starts the reading no longer reflects sugar alone.
Do I need a wort correction factor?
Some brewers find their refractometer reads slightly differently from their hydrometer on wort. If you have measured a correction factor for yours, apply it to your readings before using this calculator.
Should I still use a hydrometer?
A hydrometer gives a direct final gravity with no correction needed, so many brewers use a refractometer on brew day and a hydrometer to confirm the final reading.