Working out specific gravity and attenuation from refractometer readings.

Refractometers are great on brewday. You can take a drop or two of wort and get a half decent gravity reading. They're quite finicky after fermentation has begun though, but there are few methods to get a slightly more accurate result. Sean Terril had some calculations for this, and I've put several different methods here: *New Cubic*, *Old Cubic* and *New Linear*. You don't really need to worry about the names, just start with *New Cubic* and compare it to the hydrometer readings. If *Old Cubic* or *New Linear* are more accurate for you, use those.

- Enter your initial refractometer readings
- Enter
*either*the refractometer**or**hydrometer FG reading. If you enter a hydrometer reading, it'll use that instead of the refractometer one. - If you have a sugary (e.g. table sugar) wort - say 10% or more, change the wort correction figure. I'd drop it a point per 10% of sugar till you get to zero, so 10% = 1.03, 20% = 1.02, 40% = 1.00, 50% = 1.00.
- Look at the results in the greyed out boxes.

# Results

**Specific Gravity**: calculated SG based on your refractometer reading**ABV%**: calculated alcohol by volume percentage**Apparent Attenuation %**: density of the finished vs initial wort. This doesn't take alcohol into account when comparing the attenuation of the unfermented vs fermented wort.**Attenuation %**: actual attenuation with alcohol density being taken into consideration. This should be the measure of how much sugar in your wort got fermented.**New Cubic**: FG using the*New Cubic*calculation method.**Old Cubic**: FG using the*Old Cubic*calculation method.**New Linear**: FG using the*New Linear*calculation method.

**James Torr** 18 Jun 22