# Refractometer Correction Calculator

A refractometer correction converts a Brix reading taken during or after fermentation into true specific gravity by accounting for the refractive index of ethanol. Without correction, readings run several points high because alcohol bends light more than its concentration suggests. The Terrill cubic model fits the correction from the original gravity and the current Brix reading.

A refractometer reads high once there is alcohol in the sample. Enter your original gravity and the current Brix reading to get the real gravity.

HTML version: https://brewgravity.com/calculators/refractometer/

## Inputs

- **Original gravity (SG)** (min 1, step 0.001) — default: 1.055
- **Current refractometer reading (°Bx)** (min 0, step 0.1) — default: 7.5
- **Wort correction factor** (min 0.9, step 0.01) — default: 1.04

## Outputs

- **fg**: Corrected FG
- **abv**: ABV
- **att**: Apparent attenuation

## FAQ

### Why is my refractometer reading higher than my hydrometer?

Alcohol. The refractometer over-reads once fermentation has started, and the gap widens as the beer attenuates. The correction on this page converts the reading back to true gravity.

### Can I use a refractometer for final gravity?

For tracking, yes. For the reading you bottle against, use a hydrometer — the corrected value carries a point or two of uncertainty and priming calculations assume the fermentation really has finished.

### What is Brix?

Grams of sucrose per 100 grams of solution. It is very close to degrees Plato, which brewers use for the same thing; 1 °Bx is roughly 1.004 specific gravity in the range wort occupies.

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Source: https://brewgravity.com — Free refractometer correction calculator using the Terrill model to convert a Brix reading plus original gravity into true specific gravity, ABV and attenuation during fermentation.