Original Gravity (OG); Original Extract (OE)
The Original Gravity is the specific gravity measured before fermentation. From it the analyst can compute the Original Extract which is the mass (grams) of sugar in 100 grams of wort (°P) by use of the Plato scale. The symbol will denote OE in the formulas which follow.
I have created a simple tool, and made the source code open source, that will allow you to calculate original gravity. I also created a blog post saying how I did it.
Original Gravity Tool
Original Gravity Howto Blog Post
Why Plato instead of Brix? I know they are very close, but most of the measurement tooling I have available to me measures in Brix, which is a standard in the beverage industry.
As a homebrewer turned distiller, I still use gravity so this tool is very welcomed. Thanks for it, much appreciated. Old ways are hard to change so I'll be sticking with gravity till the TTB says I have to use brix.
It is brew centric as Panoscape mentions because I use brew process, equipment for fermentation and corn beer production. If someone has Brix conversion just comment on the blog post and I will add them to the interface.