Refractometer Calculator
Turn Brix into gravity before fermentation, and get true gravity and ABV once alcohol is in the beer. Works with any brewing refractometer.
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How to use a refractometer for brewing
- Zero it. Put a few drops of distilled water on the prism at room temperature. It should read 0. If not, turn the calibration screw.
- Before you pitch, put 2–3 drops of cooled wort on the prism and read the Brix. Use Before fermentation to turn it into gravity.
- During fermentation, read a fresh sample and enter it with your starting reading under During or after fermentation. The calculator removes the effect of the alcohol.
- Know when it’s done. Two corrected readings a day or two apart that match mean fermentation has finished.
Why refractometer readings go wrong after fermentation starts
A refractometer measures how much a sample bends light. Sugar bends light, and so does alcohol. Before fermentation there is no alcohol, so Brix converts cleanly to gravity. Once the yeast starts turning sugar into alcohol, the raw reading stays high. A beer that has really finished at 1.010 can still read about 6 °Bx, which looks like 1.024 on a chart.
This calculator uses Sean Terrill’s correction, which he built from hundreds of paired hydrometer and refractometer readings. It’s close enough to track fermentation and decide when to crash and package. For very strong beers, check the final number with a hydrometer.
Wort correction factor
Wort isn’t pure sugar water, so most refractometers read a little high on wort. The wort correction factor fixes that. 1.04 is a good starting point. To find your own, read the same unfermented wort with a hydrometer and your refractometer and use Find my correction factor. Average three or four brew days.
Brix to specific gravity chart
For wort that hasn’t started fermenting. Use the middle column if you haven’t measured your correction factor.
| Brix reading | Gravity (no correction) | Gravity (1.04 correction) | Plato (1.04 correction) |
|---|---|---|---|
| 2 | 1.008 | 1.007 | 1.9 |
| 3 | 1.012 | 1.011 | 2.9 |
| 4 | 1.016 | 1.015 | 3.8 |
| 5 | 1.020 | 1.019 | 4.8 |
| 6 | 1.024 | 1.023 | 5.8 |
| 7 | 1.028 | 1.027 | 6.7 |
| 8 | 1.032 | 1.031 | 7.7 |
| 9 | 1.036 | 1.034 | 8.7 |
| 10 | 1.040 | 1.038 | 9.6 |
| 11 | 1.044 | 1.042 | 10.6 |
| 12 | 1.048 | 1.046 | 11.5 |
| 13 | 1.053 | 1.050 | 12.5 |
| 14 | 1.057 | 1.055 | 13.5 |
| 15 | 1.061 | 1.059 | 14.4 |
| 16 | 1.065 | 1.063 | 15.4 |
| 17 | 1.070 | 1.067 | 16.3 |
| 18 | 1.074 | 1.071 | 17.3 |
| 19 | 1.079 | 1.075 | 18.3 |
| 20 | 1.083 | 1.080 | 19.2 |
| 21 | 1.087 | 1.084 | 20.2 |
| 22 | 1.092 | 1.088 | 21.2 |
| 23 | 1.096 | 1.092 | 22.1 |
| 24 | 1.101 | 1.097 | 23.1 |
| 25 | 1.106 | 1.101 | 24.0 |
| 26 | 1.110 | 1.106 | 25.0 |
| 27 | 1.115 | 1.110 | 26.0 |
| 28 | 1.120 | 1.115 | 26.9 |
| 29 | 1.124 | 1.119 | 27.9 |
| 30 | 1.129 | 1.124 | 28.8 |
Questions
How do I convert Brix to specific gravity?
For wort that hasn’t fermented, divide the Brix reading by your wort correction factor (1.04 if you don’t know it) to get degrees Plato, then convert Plato to gravity. One degree Plato is roughly 4 gravity points, so 12 °Bx ÷ 1.04 = 11.5 °P, or about 1.046.
Can I use a refractometer to check final gravity?
Yes, as long as you correct the reading. Enter the reading from before you pitched and the reading now, and the calculator takes out the effect of the alcohol. The raw number on its own will always read high once fermentation has started.
What is a wort correction factor?
It’s the ratio between what your refractometer reads on wort and the wort’s true sugar content. Most land between 1.02 and 1.06. Measure yours by reading the same unfermented wort with a hydrometer and the refractometer.
Does temperature matter with a refractometer?
Most brewing refractometers have automatic temperature compensation (ATC), so readings between about 50°F and 86°F (10–30°C) are fine. Let the drops sit on the prism for 30 seconds so they reach the prism’s temperature. Hot wort evaporates and reads high.
Why use a refractometer instead of a hydrometer?
It needs two or three drops instead of a full sample jar, so you can check a fermenter every day without losing beer. On a pressurized fermenter like our Unitank, a few drops from the sample valve is all you need.