I have written a small unit conversion library plus command line program named Ingscale in Haskell. The names stands for “Ingredient Scaler”, since it is particularly suited for the scaling of ingredients lists.

There are two modes of scaling: First, a given set of ingredients can be scaled by a fixed factor. Second, a set of ingredients can be scaled such that a particular ingredients ends up at a specified quantity. Say, you want to make a cake whose recipe requires 200g flour but you only have 150g flour. Then Ingscale can scale your ingredients list so that the resulting ingredients list requires exactly 150g. Ingscale tries to do scale your ingredients in a clever way, rounding to reasonable and easy to measure quantities, if possible. The code can be found at github. Here is the README:

This is Ingscale, a library and a command line tool for convenient scaling of ingredients lists.

Here is an example:

$ cat example.txt
Servings, 4
Soy Milk, 3 cups
Salt, 1/2 tsp
Brown Sugar, 3 1/4 tbsp
Foo Flour, 200g
Roasted Bar, 0.6 l

We can scale this ingredients list by a fixed factor, e.g.:

$ ./ingscale --scale-by 2 < example.txt
Servings, 8 
Soy Milk, 6 cup [1.42 l, 1420 ml, 288 tsp, 96 tbsp, 48 fl.oz]
Salt, 1 tsp [5.0e-3 l, 5 ml, 2.0e-2 cup, 1/3 tbsp, 0.17 fl.oz]
Brown Sugar, 6 1/2 tbsp [9.6e-2 l, 96 ml, 0.41 cup, 19 1/2 tsp, 3 1/4 fl.oz]
Foo Flour, 400 g [14 oz]
Roasted Bar, 1.2 l [1200 ml, 5 cup, 243 1/2 tsp, 81 1/4 tbsp, 40 1/2 fl.oz]

Or we can scale it to a fixed ingredient quantity, e.g.:

$ ./ingscale --scale-to "Soy Milk, 2.5 cup" < example.txt
Servings, 3 1/3 
Soy Milk, 2 1/2 cup [0.591 l, 591 ml, 120 tsp, 40 tbsp, 20 fl.oz]
Salt, 0.42 tsp [2.0e-3 l, 2 ml, 1.0e-2 cup, 0.14 tbsp, 7.0e-2 fl.oz]
Brown Sugar, 2.71 tbsp [4.0e-2 l, 40 ml, 0.17 cup, 8 1/4 tsp, 1 1/3 fl.oz]
Foo Flour, 166 2/3 g [6 oz]
Roasted Bar, 1/2 l [500 ml, 2.11 cup, 101 1/2 tsp, 33 3/4 tbsp, 17 fl.oz]

That’s about it.

The code can be built with stack, that is, “stack build” should be sufficient to build it.