Need CLI for calculating extract needed to hit target gravity

[chrisgilmerproj]

Hitting target gravity is important to getting a good beer. The equation is pretty simple:

( OG volume * OG units - current volume * current GU ) / Extract potential

If I have a beer that should enter the fermenter at 5.0 Gallons and 70 GU (1.070) and I'm currently boiling 4.0 Gallons with a 16 GU (1.016) then I'm looking at a difference of 286 GU. If I'm using Liquid extract I divide that by 38 GU/lb (or with DME it would be 45 GU/lb):

286 GU / 38 GU/lb = 7.53 lbs of liquid extract needed

It would be handy if this was either a CLI or utility to use against a pre-built recipe.

[chrisgilmerproj]

There is an additional equation that has you adjust volume instead of extract:

OG volume = ( current volume * current GU ) / OG units

An example would be if you have a lot of wort and you decide to boil it down until you get 70 GU (1.070). So you take the total gravity of the mash and divide it by that:

( 6.0 Gal * 65 GU ) / 70 GU = 5.57 Gal

This is useful if you're approaching the end of the boil and haven't hit target gravity. If you're willing to have a smaller batch of beer you can just boil it down to the volume given by this equation.