Converting SG to Brix and back
Specific gravity to degrees Brix and back, in gravity points.
Specific gravity (SG) and degrees Brix describe the same thing — the amount of extract in the wort — but they are measured with different instruments on different scales. A hydrometer gives specific gravity, a refractometer reads Brix.
Calculator
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How the scales differ
Specific gravity shows how many times denser the wort is than water: 1.052 means a litre of wort is 52 grams heavier than a litre of water. Gravity points are the same figure multiplied by a thousand: 1.052 is 52 points. Brewers like points because they are easy to calculate with: extract is directly proportional to points, so dilution and boil-off reduce to a simple proportion.
Degrees Brix are the mass fraction of dissolved sucrose as a percentage. 12 °Bx means 12 grams of sucrose in 100 grams of solution. A refractometer measures the refractive index, which for sucrose solutions is converted to Brix using the ICUMSA tables, so the Brix scale is the natural one for a refractometer.
The conversion formula
The reverse conversion from Brix to specific gravity uses a quadratic approximation. Both formulas match the Brewer’s Friend tables and are used both in the journal and in this calculator.
°Bx = −616.868 + 1111.14·SG − 630.272·SG² + 135.997·SG³ SG = 1 + °Bx / (258.6 − (°Bx / 258.2)·227.1)
Typical values
| Specific gravity | Brix |
|---|---|
| 1.040 | 9.99 °Bx |
| 1.048 | 11.91 °Bx |
| 1.052 | 12.90 °Bx |
| 1.060 | 14.74 °Bx |
| 1.070 | 17.06 °Bx |
| 1.090 | 21.57 °Bx |
What this conversion does not do
The converter translates between scales, but it does not correct measurements. A refractometer carries two errors of its own: the instrument is calibrated against sucrose while wort contains maltose and dextrins (the WCF correction), and in fermenting wort the accumulated alcohol inflates the reading. Unfermented wort can be converted directly; fermenting wort only with an alcohol correction.
- Unfermented wort before pitching: the scale conversion is correct.
- Fermenting wort: an alcohol correction is needed, or Brix will read too high.
- A hydrometer in wort that is not at 20 °C: a temperature correction is needed.