In bread baking formula are created by calculating everything as a percentage of the total flour weight. For example, if the total flour weight is 1000g then 50% hydration would be 500g.
In the case of using baker's yeast, these calculations are straight forward, but if you have a natural levain (e.g., sourdough starter) the math is more opaque because some of the total flour weight and water are part of the starter.
This program does all of the bakers math and outputs the formula in an easy to read PDF table. The folder formula shows some examples of the output.