Many hydrometers and refractometers may provide a reading in degrees Brix instead of standard gravity. Brix is simply another unit measuring the amount of dissolved sugars can be converted to standard gravity using the following calculator.
* CRITICAL THINKING *
Many homebrewers and winemakers like to use refractometers to record the Brix of a sample because of their extreme convenience over a hydrometer. However, the way that a refractometer determines Brix skews the reading when alcohol is present. This means that a refractometer is perfectly suitable for taking a reading to determine the Original Gravity (OG), but using one during and after fermentation can be inaccurate. There do exist some calculators such as the one below to help determine the corrected standard gravity based on the initial brix (no alcohol present) and the current brix (alcohol present). These calculators will get you close, but there exists some controversy in their precision. When in doubt, we encourage that best practice is to use a hydrometer any time after fermentation begins.