Here, you can calculate percentages for sourdough bread baking. Use the left boxes to adjust percentages (while total dough weight is held constant), or the right boxes to adjust weights. Changing levain percentage tries to maintain flour to water ratio without changing the amount of dough you get. Changing hydration percentage tries to maintain levain ratio, also without changing the amount of dough you get.

Notes: the above percentages are total percentages, i.e. everything is with respect to dough weight. If we were talking baker's percentages (w.r.t flour weight), then the above percentage would translate to water 75%, levain 20% and hydration of 85%.

This calculation ommits salt as negligible. Adding a teaspoon of salt would amount to 0.3% difference.