🔭 Refractometer Final Gravity Calculator
Enter the original Brix, the current Brix reading and your correction factor to estimate the true final gravity and ABV.
Corrected final gravity
1.015
Original gravity
1.046
Estimated ABV
4.2%
Alcohol bends light differently from sugar, so once fermentation starts a refractometer reads final gravity too high — you can't just convert the Brix. This applies the Wort Correction Factor (WCF, typically ~1.04, calibrate yours against a hydrometer) and Sean Terrill's cubic to estimate the true final gravity from the original and current Brix. It's an estimate; confirm important readings with a hydrometer. 🔒 In your browser.
How the refractometer final gravity calculator works
Refractometers are quick and need only a drop of sample, but alcohol bends light differently from sugar, so once fermentation starts they read the final gravity too high. The tool applies a wort correction factor and Sean Terrill's cubic formula to estimate the true final gravity from your original and current Brix readings — and works out the ABV.
The wort correction factor (WCF) is specific to your refractometer — around 1.04 is typical, but calibrate yours by comparing a pre-fermentation refractometer reading against a hydrometer. The correction is an estimate that assumes a normal fermentation; for a reading that really matters (a competition, a big beer), confirm it with a hydrometer.
Frequently asked questions
Why can't I use a refractometer for final gravity directly?
Because alcohol refracts light differently from sugar, inflating the reading once fermentation begins. A raw Brix-to-gravity conversion then reads the final gravity too high — you need an alcohol correction like this one.
How does the refractometer correction work?
It takes your original and current Brix, divides them by a wort correction factor (WCF) specific to your device, and applies Sean Terrill's cubic formula to estimate the true final gravity accounting for the alcohol present.
What is the wort correction factor?
A per-refractometer adjustment (typically ~1.04) that aligns its Brix scale with actual gravity. Calibrate it by measuring an unfermented wort with both the refractometer and a hydrometer and dividing to find your factor.
How accurate is the estimate?
Good enough for tracking a fermentation and ballparking ABV, but it's a model, not a direct measurement. For readings that matter — a competition entry or a very strong beer — confirm with a hydrometer.
Can I track fermentation progress with a refractometer?
Yes — that's a great use. A few drops each day, run through this correction, shows the gravity falling and stabilising, telling you when fermentation is complete without drawing large hydrometer samples.