What each scale is
- Specific gravity — density relative to water. 1.050 means 5% denser than water. Standard among homebrewers in Britain and America.
- Degrees Plato — percentage of dissolved solids by weight. 12 °P means 12 grams of extract per 100 grams of wort. Standard in commercial brewing and across most of Europe.
- Brix — the same weight-percent idea, calibrated for sucrose. What a refractometer reports.
- Gravity points — just specific gravity with the leading 1.0 stripped off. 1.050 is 50 points. Convenient for arithmetic.
The conversions
The cubic is the ASBC standard fit. It is accurate well past any gravity a homebrewer will reach.
Brix and Plato
Brix and Plato are defined against slightly different reference tables, but across the range brewers work in they differ by less than a tenth of a degree. Treating them as interchangeable is standard practice and is what this calculator does.
The important caveat is not the scale — it is the instrument. A Brix reading from a refractometer is only trustworthy before fermentation starts. Afterwards it needs correcting for alcohol.
Why Plato is worth knowing
Specific gravity is easier to read off a hydrometer, but Plato is easier to reason with. Because it is a weight percentage, attenuation and yeast pitching rates are both naturally expressed in Plato, and the arithmetic works out without fudge factors. Most published pitching rates are in cells per millilitre per degree Plato for exactly this reason.