Why do refractometer readings need correction?

Refractometers measure the refractive index of a liquid. Alcohol has a different refractive index to sugar, so once fermentation begins and alcohol is present, the refractometer reading no longer accurately represents the sugar content. The correction formula accounts for this.

What is the wort correction factor (WCF)?

Wort is not a pure sucrose solution, so refractometers (calibrated for sucrose) read slightly high. The WCF corrects for this — typically 1.04 for most refractometers. You can calibrate yours by comparing a refractometer reading to a hydrometer reading of the same wort sample.

Can I skip the correction for pre-fermentation readings?

Pre-fermentation readings only need the wort correction factor (WCF), not the alcohol correction. The full alcohol correction is only needed once fermentation has started and alcohol is present in the sample.

How accurate is the refractometer correction?

The Sean Terrill cubic formula used here is accurate to within 0.001-0.002 SG for most normal-strength beers. Accuracy decreases slightly for very high gravity beers above 1.080 OG. For the most precise readings, always confirm final gravity with a hydrometer.

Why does my corrected FG seem wrong?

Common causes include: incorrect original Brix reading, not applying the wort correction factor, or a refractometer that needs recalibration. Always calibrate your refractometer with distilled water before each use, and double-check your OG reading was accurate.

BrewCalcs

Refractometer Correction Calculator

Correct refractometer readings for alcohol presence during and after fermentation.

Original Brix (pre-fermentation)

Current Brix (during/after fermentation)

Wort Correction Factor

Default 1.04 — calibrate with your refractometer

How We Calculate This

The Correction Formula

This calculator uses Sean Terrill's cubic correction formula, which is widely regarded as the most accurate method for correcting refractometer readings during fermentation. It accounts for the non-linear relationship between alcohol content and refractive index.

Wort Correction Factor

The default WCF of 1.04 works for most refractometers. To calibrate: take a wort sample before pitching, read it on both your refractometer and hydrometer. Divide refractometer Brix by the hydrometer-derived Brix to get your WCF.

Frequently Asked Questions

Related Calculators

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Final Gravity Calculator

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Brix to SG Converter

Convert Brix refractometer readings to specific gravity.

Plato to SG Converter

Convert degrees Plato to specific gravity and back.

Last updated: 2025-02-20

All calculations are estimates. Always verify values and adjust based on your equipment and ingredients.